[media] saa7134: v4l2-compliance: implement V4L2_CAP_DEVICE_CAPS

Make saa7134 driver more V4L2 compliant: implement V4L2_CAP_DEVICE_CAPS support
and fix all capabilities problems reported by v4l2-compliance.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>