Support for RAK 4630

[kravietz]

Trying to deploy embassy blinky example to RAK 4630 using U2F method, but I'm getting this:

$ elf2uf2-rs --deploy --serial --verbose target/thumbv7em-none-eabi/release/blinky blinky.u2f
Found pico uf2 disk /media/user/RAK4631
Error: "entry point is not in mapped part of file"

Happy to do a PR but I'd need some guidance on what should be mapped where - possibly the required addresses could be taken from https://github.com/meshtastic/firmware/blob/master/bin/uf2conv.py