regulator: MAX77686: Add Maxim 77686 regulator driver

Add driver for support max77686 regulator.
MAX77686 provides LDOs[1~26] and BUCKs[1~9]. It support to set or get the
volatege of regulator on max77686 chip with using regmap.

Signed-off-by: Chiwoong Byun <woong.byun@samsung.com>
Signed-off-by: Jonghwa Lee <jonghwa3.lee@samsung.com>
Signed-off-by: Myungjoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Yadwinder Singh Brar <yadi.brar@samsung.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>