Port x264 deblocking code to libavcodec.  This includes SSE2 luma deblocking code and both MMXEXT and SSE2 luma intra deblocking code for H.264 decoding.  This assembly is available under --enable-gpl and speeds decoding of Cathedral by 7%.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@16239 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b