media: mpeg2-ctrls.h: move MPEG2 state controls to non-public header

The MPEG2 state controls for the cedrus stateless MPEG2 driver are
not yet stable. Move them out of the public headers into media/mpeg2-ctrls.h.

Eventually, once this has stabilized, they will be moved back to the
public headers.

Unfortunately I had to cast the control type to a u32 in two switch
statements to prevent a compiler warning about a control type define
not being part of the enum.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>