power: regulator: Add support for regulator-force-boot-off

Add support for regulator-force-boot-off DT property.
This property can be used by the board/device drivers for
turning off regulators on early init stages as pre-requisite
for the other components initialization.

Signed-off-by: Konstantin Porotchkin <kostap@marvell.com>
Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Jaehoon Chung <jh80.chung@samsung.com>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>