lavc: Move prediction_method to codec private options

This options is only used by huffyuv, ffvhuv, jpegls, mjpeg,
mpegvideoenc, png, utvideo.
It is a very codec-specific options, so deprecate the global variant.
Set proper limits to the maximum allowed values, and update utvideoenc
tests to use the new option name.

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>
