[media] dvbdev: add support for interfaces

Now that the infrastruct for that is set, add support for
interfaces.

Please notice that we're missing two links:
	DVB FE intf    -> tuner
	DVB demux intf -> dvr

Those should be added latter, after having the entire graph
set. With the current infrastructure, those should be added
at dvb_create_media_graph(), but it would also require some
extra core changes, to allow the function to enumerate the
interfaces.

Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>