power: regulator: max77663: add regulator support

The driver provides regulator set/get voltage
enable/disable functions for MAXIM MAX77663 PMICs.

Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>