power_supply: Add charger driver for MAX8997/8966

MAX8997/8966 chip is a multi-function device which includes
PMIC, RTC, Fuel Gauge, MUIC, Haptic, Flash control, and
Battery charging control.
The driver for it is located at drivers/mfd.

This patch supports battery charging control of MAX8997/8966 chip and
provides power supply class information to userspace.

Signed-off-by: Donggeun Kim <dg77.kim@samsung.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: KyungMin Park <kyungmin.park@samsung.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>