media: ov5640: Implement get_selection

Implement the get_selection pad operation for the OV5640 sensor driver.

The supported targets report the sensor's native size, the active pixel
array size and the analog crop rectangle from which the image is
produced.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>