[media] omap_vout: convert g/s_crop to g/s_selection

This is part of a final push to convert all drivers to g/s_selection.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>