mfd: act8945a: Add Active-semi ACT8945A PMIC MFD driver

This patch adds support for the Active-semi ACT8945A PMIC.
It is a Multi Function Device with the following subdevices:
 - Regulator
 - Charger

It is interfaced to the host controller using I2C interface,
ACT8945A is a child device of the I2C.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Acked-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>