update ffmpeg (n0.8-19508-g454c5d1)

Notes: broken atm because our custom files need to be updated too

* libavcodec/h264_dxva.c
* libavcodec/h264_recov.c
* libavcodec/vc1_dxva.c
remove custom code
n0.8-19540-g715c230
update CFLAGS and ffmpeg/config.asm and ffmpeg/config.h