media: v4l2-rect.h: add position and equal helpers

Add two helper functions to check if two rectangles have the same
position (top/left) and if two rectangles equals (same size and
same position).

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>