[media] dt: bindings: Add lane-polarity property to endpoint nodes

Add lane-polarity property to endpoint nodes. This essentially tells that
the order of the differential signal wires is inverted.

Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>