V4L/DVB (11073): au0828: disable VBI code since it doesn't yet work

Since the VBI support is not yet working for the au0828, don't advertise the
capability or create the /dev/vbi device.

Signed-off-by: Devin Heitmueller <dheitmueller@linuxtv.org>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>