[media] v4l2-rect.h: new header with struct v4l2_rect helper functions

This makes it easier to share this code with any driver that needs to
manipulate the v4l2_rect datastructure.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>