charger: bq25180: add control for battery charge limit

The linear battery charger will charge the connected battery up
to a specific voltage. This is different depending on the chemistry
of the battery. Most LiPo Batteries have a nominal voltage of 4.2V,
which is why the default voltage of the bq25180 is 4.2V.

Signed-off-by: Fabian Pflug <fabian.pflug@grandcentrix.net>