power: supply: bq25890: Add support for setting bq25890 and bq25896's VINDPM

The bq25890 has low voltage protection on VIN. Allow the register
to be set from the device tree.

Signed-off-by: Eric Kuzmenko <eric.kuzmenko@puri.sm>
Signed-off-by: Angus Ainslie (Purism) <angus@akkea.ca>