Add optional reset and standby gpios. The reset gpio is used to reset
the chip in power_on().

The standby gpio is not used currently. It is just unset, so the chip is
not in standby.
Signed-off-by: NMarkus Pargmann <mpa@pengutronix.de>
Reviewed-by: NPhilipp Zabel <p.zabel@pengutronix.de>
Acked-by: NRob Herring <robh@kernel.org>
Acked-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@osg.samsung.com>