HAL_QURT: revived QURT HAL

[tridge]

This is a revival of the old QURT HAL for the new ModalAI boards, testing on a starling dev copter

this builds on #27504

Issues:

• mavlink bridge doesn't support ArduPilot specific mavlink XML
• fix so name libslpi_hello_world.so to some other name
• UDP fwding in ap_host sometimes stops
• sl_client_config_uart needs to be fixed to not have side effects for invalid baudrate
• doesn't yet build ARM frontend app
• only getting ESC telem from 3 ESCs (check ESC fw version and config?)
• scripting not working
• storage takes a long time to sync
• not getting current from ESC telem
• need to implement ESC power API
• should have a default param file
• need to fix reboot
• getting corrupt MAVLink pkts from ap_host
• need to test VIO, rangefinder, flow etc
• reduce number of build warnings with clang
• setup CI for qurt.ardupilot.org
• why the 2048 offset in current?

Testing:

• use ./waf configure --board QURT
• build: ./waf copter

[rmackay9]

MP's parameter loader apparently can't see files below the "Frame_params" directory so perhaps we should move this up and add a prefix. E.g. "ModalAI_AutonomyDevKit.parm"

[tridge]

as discussed on the call, once merged I will do a MissionPlanner PR to support this directory, like I did for quadplanes

[rmackay9]

We should add pages to the developer wiki to clarify how to setup the build environment

[davidbuzz]

this PR seems to rely elmost entirely on POSIX pthread/s , and I wonder if it shouldn't be called AP_HAL_PTHREADS or AP_HAL_POSIX, or have an intermediate layer for the pthreads and/or posix related stuff... especially since other hal/s like Linux and ESP32 both have posix and pthreads support.

eg esp32 pthreads support here: https://docs.espressif.com/projects/esp-idf/en/stable/esp32/api-reference/system/pthread.html

That's more of a suggestion for the future tho, not a stopper for this PR, which clearly works well-enough to merge.

[peterbarker]

LGTM apart from the very minor things raised.