mfd: MAX8997/8966 support

MAX8997/MAX8966 chip is a multi-function device with I2C bussses. The
chip includes PMIC, RTC, Fuel Gauge, MUIC, Haptic, Flash control, and
Battery (charging) control.

This patch is an initial release of a MAX8997/8966 driver that supports
to enable the chip with its primary I2C bus that connects every device
mentioned above except for Fuel Gauge, which uses another I2C bus. The
fuel gauge is not supported by this mfd driver and is supported by a
seperated driver of MAX17042 Fuel Gauge (yes, the fuel gauge part is
compatible with MAX17042).

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>