charger: bq25180: add support for recharge voltage threshold

The battery charger will stop charging the battery if it believes,
that is is completely charged. If the battery drops below a certain
voltage threshold, then the battery charger starts charging the
battery again.

For the bq25180 the threshold can only be one of either 100mV or
200mV below the VSET voltage.

See table 8-16 Bit 5 in https://www.ti.com/lit/ds/symlink/bq25180.pdf



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