v4l2: fix an assert issue

for the buffers within range of [m_actualOutBufferCount, m_maxBufferCount[OUTPUT]]
there are not used in reality, but still be returned back to client during flush (seek/eos)
vp8enc: init version for hardware decoder support i/p frame, hard written filter level and quant index
tests: revert XInitThreads() in yamidecode -- need more investigation

- it breaks yamidecode test, X11 call blocks at XGetWindowAttributes()
  after va dlopen() i965 driver. it is strange.
- mp4/h264 files still breaks in yamidecode
- however, mp4/h264 files can work in v4l2decode test
seems, yamidecode is single thread, we needn't call XInitThreads().
tests: fixes for v4l2decode to use avformat for mp4/h264