[media] dvb-core: be sure that drivers won't use DVBv3 internally

Now that all frontends are implementing DVBv5, don't export the
DVBv3 specific stuff to the drivers. Only the core should be
aware of that, as it will keep providing DVBv3 backward compatibility.

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