media: extended-controls.rst: update the mpeg2 compound controls

The layout of the compound controls has changed to fix
32/64 bit alignment issues and the use of timestamps instead of
buffer indices to refer to buffers.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>