ffmpeg: don't use hardcoded lookup tables

ffmpeg: don't use hardcoded lookup tables

ffmpeg can generate lookup tables at build time instead of runtime, but this is
no longer a recommended option.  The size impact is significant (12% of the
total libavcodec size, nearly 2MB), the runtime impact of dynamic tables isn't
too costly, and only a few codecs actually use the pre-generated tables (MP3,
notably).

(From OE-Core rev: 51f13afe669638dbf72f464f243adccb22be3d21)

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>