power: act8945a: add charger driver for ACT8945A

This patch adds new driver for Active-semi ACT8945A ActivePath
charger (part of ACT8945A MFD driver) providing power supply class
information to userspace.

The driver can be configured through DT (such as, total timer,
precondition timer and input over-voltage threshold).

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
[ add "|| COMPILE_TEST" to MFD_ACT8945A dependency ]
Signed-off-by: Sebastian Reichel <sre@kernel.org>