WIP - RP2350 with Nuttx master

[vidma]

Solved Problem

RP2350 / Raspberry Pico 2 support. ❗ work in progress, there's plenty stuff to fix and cleanup still!

Fixes #24187

Solution

• Use NuttX master for now (can quite easily switch back to px4 backport branch if needed)
  • depend on Nuttx master for RP2350 - WIP NuttX#332 - https://github.com/vidma/PX4-NuttX/tree/px4_master
  • added some helpers / minimal changes to make PX4 compatible with newest nuttx
  • make these changes configurable if needed (to support both newest nuttx vs 10.3 nuttx backport) ?
• Add RP2350 support, for now limited support. Testing on Pimoroni 2 Plus.
  • UART0: console/nsh ✅
  • UART1: mavlink ✅
  • UART0/1: expresslrs RCIN - ❔ not tested yet (could be mavlink with ELRS mavlink)
  • usb serial - not working yet ( but /dev/ttyACM0 appears)
  • SPI IMU / PWM out - ❔ not working, not tested or not configured yet
  • I2C IMU GY-91 - detected, partially working (not sure if events received yet) 🟡
  • mount part of QSPI flash for persistent params storage (smartfs; added rp23xx_flash_mtd.c) 🟡
  • basic PX4 functionality, params etc - not tested or failing