media: ov2740: Add powerdown GPIO support

The ov2740 sensor has both reset and power_down inputs according to
the datasheet one or the other should always be tied to DOVDD but on
some designs both are attached to GPIOs.

Add support for controlling both a reset and a powerdown GPIO.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Tested-by: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>
Acked-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>