Add initial LoRa support on Flex

[PaulZC]

• Note: Flex LoRa is currently crippled by the way LoRa_EN and LoRa_NRST are interconnected
  • It is possible to enable LoRa by:
    • Removing T9
    • Soldering a 1uF cap between LoRa_NRST and GND (T9 pin 3 to pin 2)
    • Inverting gpioExpanderSwitch_LoraEnable (TCA9534_IO4_LoRa_EN needs to be LOW to set LoRa_EN HIGH)
• Adds a dedicated passthrough mode for Flex GNSS updates
  • Note: LG290P updates fail due to possible autobaud detection in QGNSS
  • The next Flex motherboard will have a dedicated hardware path from USB to GNSS UART1 for trouble-free updates