This helps removing the flicker, but if the battery is connected AFTER connecting the USB it will be unavailable.
A complete power cycle needs to be performed to recover charging/battery functionality.

HW flow control is still not working, probably some low lovel work is needed.

PMIC initialization is now handled by the GSM init() if the selected board is suitable. The only hadcoded PMIC initialization is 500mA maximum charge current.

PMIC handling needs to be decided; if we use the SDU method we could have troubles.
Probably the best way is using sercoms directly.
Anyway, the defaults SHOULD be almost ok (except the maximun charging current)

This commit enables PWM on pin 11 instead of pin A4 on MKR1000 improving UNO pinout compatibility

The pin mapping is still subject to change, better to not distribute
files that are not final.