regulator: act8865: Add support for act8600 charger

This provides a way to monitor battery charge status via the power
supply subsystem.

Signed-off-by: Maarten ter Huurne <maarten@treewalker.org>
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20190723011418.29143-1-paul@crapouillou.net
Signed-off-by: Mark Brown <broonie@kernel.org>