- add new SYS_HAS_GPS parameter

 - IMU init requires valid published data (device ids, etc)
 - orb_group_count will include advertised instances before data is published, so this can't be used to throttle IMU init attempts

 - mark calibration slots active for first N sensors found
 - calibration procedure don't bother resetting unused slots

 - parameter updates can be quite expensive because they trigger nearly all modules to reload all of their parameters immediately
 - limit modules from updating faster than once per second

 - the purpose is to ensure that every WorkItem (and WorkItems scheduled
by WorkItems) is allowed to run to completion every step
 - per workqueue register a lockstep component whenever a work item is
added (if not already registered)
 - once the work queue is empty unregister component

 - ekf2 selector don't register lockstep until first attitude publication
 - sensors module register lockstep component
 - enable multi-EKF2 in SITL

 - ekf2 can now run in multi-instance mode (currently up to 9 instances)
    - in multi mode all estimates are published to alternate topics (eg estimator_attitude instead of vehicle_attitude)
 - new ekf2 selector runs in multi-instance mode to monitor and compare all instances, selecting a primary (eg N x estimator_attitude => vehicle_attitude)
 - sensors module accel & gyro inconsistency checks are now relative to the mean of all instances, rather than the current primary (when active ekf2 selector is responsible for choosing primary accel & gyro)
 - existing consumers of estimator_status must check estimator_selector_status to select current primary instance status
 - ekf2 single instance mode is still fully supported and the default

Co-authored-by: Paul Riseborough <gncsolns@gmail.com>

If set, stores calibration parameters in separate storage /fs/mtd_caldata.

Signed-off-by: Silvan Fuhrer <silvan@auterion.com>

 - if valid temperature unavailable then use ICAO Standard Atmosphere 15 degrees celcius

 - new sensors work item that subscribes to N x sensor_gps and publishes vehicle_gps_position
 - blending is now configurable with SENS_GPS_MASK and SENS_GPS_TAU

Co-authored-by: Jacob Crabill <jacob@volans-i.com>
Co-authored-by: Jacob Dahl <dahl.jakejacob@gmail.com>

 - inconsistency checks now run continuously instead of only preflight
 - keep inconsistencies for all sensors
 - add per sensor data validator state as overall health flag

 - CAL_ACCx_EN -> CAL_ACCx_PRIO
 - CAL_GYROx_EN -> CAL_GYROx_PRIO
 - CAL_MAGx_EN -> CAL_MAGx_PRIO

 - purge all reminaing magnetometer IOCTL usage
 - mag calibration add off diagonal (soft iron) scale factors

 - don't bother running baro aggregator if SYS_HAS_BARO disabled

 - keep the thread within the current NuttX max length

 - remove all remaining IOCTLs for accel and gyro and handle all calibration entirely in sensors module with parameters
 - sensor_accel and sensor_gyro are now always raw sensor data
 - calibration procedures no longer need to first clear existing values before starting
 - temperature calibration (TC) remove all scale (SCL) parameters
    - gyro and baro scale are completely unused
    - regular accel calibration scale can be used (CAL_ACC*_xSCALE) instead of TC scale

 - add perf counters for monitoring

 - IMU integration move from drivers (PX4Accelerometer/PX4Gyroscope) to sensors/vehicle_imu 
 - sensors: voted_sensors_update now consumes vehicle_imu
 - delete sensor_accel_integrated, sensor_gyro_integrated
 - merge sensor_accel_status/sensor_gyro_status into vehicle_imu_status
 - sensors status output minor improvements (ordering, whitespace, show selected sensor device id and instance)

Running the sensors module out of the same WQ thread as the estimator, position, and attitude controllers is a bit safer and prevents potential priority and starvation issues. There is a very small increase in latency (~50 us) between sensors and ekf2 execution (on average). This also saves a little bit of memory (~ 3 kB) and cpu (~1-1.5% depending on the board).

The bulk of this change was tightly coupled and needed to be deleted in one pass. Some of the smaller changes were things that broke as a result of the initial purge and subsequently fixed by further eradicating unnecessary platform differences. Finally, I deleted any dead code I came across in the related files I touched while going through everything.

 - DriverFramework (src/lib/DriverFramework submodule) completely removed
 - added dspal submodule in qurt platform (was brought in via DriverFramework)
 - all df wrapper drivers removed
 - all boards using df wrapper drivers updated to use in tree equivalents
 - unused empty arch/board.h on posix and qurt removed
 - unused IOCTLs removed (pub block, priv, etc)
 - Integrator delete methods only used from df wrapper drivers
 - commander: sensor calibration use "NuttX version" everywhere for now
 - sensors: update to px4_{open, read, close} instead of DevMgr wrapper (adc open for analog differential pressure)
 - battery_status: update to px4_{open, read, close} instead of DevMgr wrapper (adc open for analog differential pressure)
 - cdev cleanup conflicting typedefs and names with actual OS (pollevent_t, etc)
 - load_mon and top remove from linux boards (unused)
 - delete unused PX4_MAIN_FUNCTION
 - delete unused getreg32 macro
 - delete unused SIOCDEVPRIVATE define
 - named each platform tasks consistently
 - posix list_devices and list_topics removed (list_files now shows all virtual files)

and remove the px4_ prefix, except for px4_config.h.

command to update includes:
for k in app.h atomic.h cli.h console_buffer.h defines.h getopt.h i2c.h init.h log.h micro_hal.h module.h module_params.h param.h param_macros.h posix.h sem.h sem.hpp shmem.h shutdown.h tasks.h time.h workqueue.h; do for i in $(grep -rl 'include <px4_'$k src platforms boards); do sed -i 's/#include <px4_'$k'/#include <px4_platform_common\/'$k/ $i; done; done
for in $(grep -rl 'include <px4_config.h' src platforms boards); do sed -i 's/#include <px4_config.h/#include <px4_platform_common\/px4_config.h'/ $i; done

Transitional headers for submodules are added (px4_{defines,log,time}.h)