power_supply: Add support for Richtek RT9455 battery charger

Based on the datasheet found here:
http://www.richtek.com/download_ds.jsp?p=RT9455



Signed-off-by: Anda-Maria Nicolae <anda-maria.nicolae@intel.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski.k@gmail.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>