power: supply: bq24735: move down bq24735_{en,dis}able_charging

bq24735_enable_charging() needs to call bq24735_config_charging(),
which is something to change later, this is just a preparatory patch.

Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Sebastian Reichel <sre@kernel.org>