V4L/DVB (4188): Add new MPEG control/ioctl definitions to videodev2.h

The old, experimental, VIDIOC_S/G_CODEC API to pass MPEG parameters is now
obsolete and is replaced by 'extended controls' which offer more flexibility
and are hopefully more future proof.
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>