Support reading packed YUV422 10bit samples from Sveriges Television AB (SVT)
which have AFAIK been created for the jvt:
I have called the format v210x due to its similarity to v210, note though I have
not confirmed that v210x is different from actual v210 samples it just is
different from the description of v210 I am aware of.
Originally committed as revision 18654 to svn://svn.ffmpeg.org/ffmpeg/trunk