The GPIOD API can be used from boardcode, so that the DT check can be
removed. To avoid breaking existing boardcode, _optional() variant has been
chosen. For completely removing the DT check, the regulator has also been
made optional, so that it could be supplied from boardcode.

As a side-effect the patch fixes the after-probe reset GPIO state, so that
the device is not kept in reset state.
Signed-off-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>