[media] saa7146: fix querycap, vbi/video separation and g/s_register

The querycap ioctl returned an incorrect version number and incorrect
capabilities (mixing up vbi and video caps).

The reason for that was that video nodes could do vbi activities: that
should be separated between the vbi and video nodes.

There were also a few minor problems with dbg_g/s_register that have
been resolved. The mxb/saa7146 driver now passes the v4l2_compliance tests.

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