* Add a new .dtsi for setting up nRF52 boot mode/retained memory
settings
* Adjust XIAO BLE to use the new include file
* Add boot mode to to the nice!nano
Upgrade the nice!nano board to HWMv2, under the proper nicekeyboards
vendor directory, and with proper revisions. Includes a breaking change
to default the `2.0.0` version instead of the much older v1 (`1.0.0`).