avcodec/mpegvideo: Deprecate mpeg_quant option for codecs != MPEG-4

avcodec/mpegvideo: Deprecate mpeg_quant option for codecs != MPEG-4

mpeg_quant may only be set for MPEG-4 and MPEG-2, yet for the latter
it is no option as the code acts as if it were always set.
So deprecate the option for all codecs for which it makes no sense.

Furthermore, given that the code already errors out if the option is set
for a codec that doesn't support it we can restrict the range of
the option for all these codecs without breaking something. This means
that the checks for whether mpeg_quant is set for these codecs can be
removed as soon as AVCodecContext.mpeg_quant is removed.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>