[media] ivtv: disable a bunch of ioctls that are invalid for the decoder VBI

The VBI capture for the decoder (/dev/vbi8) is special in that it captures
the VBI stream embedded in an MPEG stream that is being decoded.
A lot of the ioctls that would normally be valid have to be disabled since
they make no sense for such a device, and v4l2-compliance will complain
about that.

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