Initially a copy of BQ24780S

- clean up bq24715 driver
- set sane defaults for Librem14 board
- enable charger (3-cell hardcoded battery for now, take care!)
- adapt charger current and voltage based on runtime values
- improve charge handling, auto detecting 3-cell and 4-cell batteries
- try to be more careful with the charger
- charger precautions
- improve (fix) charge disabling

Signed-off-by: Matt DeVillier <matt.devillier@puri.sm>