There are many problems of current qsv trellis option:
1. Duplicated with AVCodecContext definition
2. MFX_TRELLIS_XXX is introduced by MSDK API 1.17
   Currently Without MSDK API checking thus may cause compilation issue.
3. user is inclined to enable trellis when set "-trellis 1", but
   actually it is to disable since MFX_TRELLIS_OFF is equal to 1.
4. It is too complex for user to enable trellis for every frame(I/P/B).

Just simply remove the private option, and switch to the AVCodecContext
definition. Compatibility should not a big problem (except can't exact map)
since the option name is same as AVCodecContext.
Signed-off-by: Zhong Li <zhong.li@intel.com>
Reviewed-by: Carl Eugen Hoyos <ceffmpeg@gmail.com>
Reviewed-by: Moritz Barsnick <barsnick@gmx.net>