Add support for the .get_selection() pad operation to the ov2685 sensor
driver.

Report the native sensor size (pixel array), the crop bounds (readable
pixel array area) and the current and default analog crop rectangles.
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>