mfd: Add MAX77693 driver

This patch adds MFD driver for MAX77693 to enable its sub devices.

The MAX77693 is a multi-function devices. It includes PMIC,
MUIC(Micro USB Interface Controller), flash LED control and
haptic motor control.

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
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>