Bootloader support

[luisan00]

Bootloader Support
This feature is necessary if we want to update the firmware directly from the master MCU (esp32).
Without a bootloader in the radio module we can only flash the firmware through the JTAG interface.

[jeandudey]

We have some options here:

1. Enable bootloader support using CCFG settings (unportable, only works with CC13x2, CC26x2) devices. This requires CCFG ability to be linked and flashed. This is good in case the or other does not work, or the firmware gets corrupted (this bootloader resides in ROM, and thus, can't be changed nor corrupted).
2. Use riotboot, this could enable us to do OTA firmware updates (trough SLIP or air). Requires more testing and isn't very stable yet (something we can improve in the long term).
3. mcuboot, untested, I don't know if it works with RIOT currently but might be a good option to consider in case we can't get riotboot to work.