[media] go7007: standardize MPEG handling support

The go7007 produces elementary streams, so we shouldn't use the STREAM_TYPE
control, since that is for multiplexed streams.
Instead use V4L2_PIX_FMT_MPEG1/2/4.
Initially set up all the values for MPEG-2 dvd-mode, and select the dvd_mode
field if those values match that setup precisely.
Clean up lots of obsolete code relating to the custom ioctls for the MPEG
support.

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