[media] dvbdev: enable DVB-specific links

For now, let's keep the DVB-specific media controller links enabled
by default. On most devices, this is fixed anyway, so no big issue.

Ok, the demux actually have dynamic links based on the filters, but
we don't represent them yet, as the media controller currently lacks
the capability of dynamically create/delete entities.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>