dm: pmic: add max77686 pmic driver

dm: pmic: add max77686 pmic driver

This is the implementation of driver model PMIC driver.
The max77686 PMIC driver implements read/write operations and driver
bind method - to bind its childs.

This driver will try to bind the regulator devices by using it's child
info array with regulator prefixes and driver names. This should succeed
when compatible regulator driver is compiled. If no regulator driver found,
then the pmic can still provide read/write operations, and can be used with
PMIC function calls.

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Acked-by: Simon Glass <sjg@chromium.org>