[media] em28xx: disable tuner related ioctls for video and VBI devices without tuner

Disable the ioctls VIDIOC_G_TUNER, VIDIOC_S_TUNER, VIDIOC_G_FREQUENCY and
VIDIOC_S_FREQUENCY for video and VBI devices without tuner.

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>