- no longer start sercon or mavlink usb by default
- on USB connection (VBUS) monitor serial USB at low rate and start Mavlink if there's a HEARTBEAT or nshterm on 3 consecutive carriage returns
- the mavlink USB instance is automatically stopped and serdis executed if USB is disconnected
- skipping Mavlink USB (and sercon) saves a considerable amount of memory on older boards
- include icm20948 on most boards by default
- create more test variants for default boards near flash limit (cuav_nora_test, cuav_x7pro_test, holybro_durandal-v1_test)
- fix UART config (GPS1, etc)
- TELEM2 enable TX DMA
- init simplify (sync with CubeOrange)
- amber LED use for armed state
- manually start ak09916 (Here2) on I2C2 with proper rotation