[media] saa7134-empress: add missing MPEG controls

Reported by, and based on a patch from, Martin Dauskardt.

The AUDIO_AC3_BITRATE control is still missing from this list, but such
optional controls are a bit hard to handle. This will be fixed automatically
when we switch to the control framework.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Reported-by: Martin Dauskardt <martin.dauskardt@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>