media: ov2680: Check for "powerdown" GPIO con-id before checking for "reset" GPIO con-id

The datasheet of the OV2680 labels the single GPIO to put the sensor in
powersaving mode as XSHUTDN aka shutdown, _not_ reset.

This is important because some boards have standardized sensor connectors
which allow connecting various sensor modules. These connectors have both
reset and powerdown signals and the powerdown signal is routed to
the OV2680's XSHUTDN pin.

On x86/ACPI multiple Bay Trail, Cherry Trail, Sky Lake and Kaby Lake models
have an OV2680 connected to the ISP2 / IPU3. On these devices the GPIOS are
not described in DT instead the GPIOs are described with an Intel specific
DSM which labels them as either powerdown or reset. Often this DSM returns
both reset and powerdown pins even though the OV2680 has only 1 such pin.

For the ov2680 driver to work on these devices it must use the GPIO with
"powerdown" as con-id, matching the XSHUTDN name from the datasheet.

As for why "powerdown" vs say "shutdown" the ACPI DSM -> con-id mapping
code is shared, so we must use standardized names and currently all of
the following sensor drivers already use "powerdown":
adv7180, gc0310, isl7998x, ov02a10, ov2659, ov5640, ov5648, ov5670,
ov5693, ov7670, ov772x, ov7740, ov8858, ov8865 and ov9650 .

Where as the hi846 driver is the lonely standout using "shutdown".

Try the "powerdown" con-id first to make things work, falling back to
"reset" to keep existing DT setups working.

Acked-by: Rui Miguel Silva <rmfrfs@gmail.com>
Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>