multimedia/gstreamer1-libav: unbreak FFMPEG=off with CPUTYPE >= haswell

In file included from libavcodec/hevc_cabac.c:27:
In file included from libavcodec/cabac_functions.h:46:
libavcodec/x86/cabac.h:193:9: error: inline assembly requires more registers than available

BRANCHLESS_GET_CABAC("%0", "%q0", "(%4)", "%1", "%w1",
^

libavcodec/x86/cabac.h:143:9: note: expanded from macro 'BRANCHLESS_GET_CABAC'

"movzbl "statep"    , "ret"                                     \n\t"\
^

libavcodec/x86/cabac.h:193:9: error: inline assembly requires more registers than available
libavcodec/x86/cabac.h:143:9: note: expanded from macro 'BRANCHLESS_GET_CABAC'

"movzbl "statep"    , "ret"                                     \n\t"\
^

libavcodec/x86/cabac.h:193:9: error: inline assembly requires more registers than available
libavcodec/x86/cabac.h:143:9: note: expanded from macro 'BRANCHLESS_GET_CABAC'

"movzbl "statep"    , "ret"                                     \n\t"\
^

libavcodec/x86/cabac.h:193:9: error: inline assembly requires more registers than available
libavcodec/x86/cabac.h:143:9: note: expanded from macro 'BRANCHLESS_GET_CABAC'

"movzbl "statep"    , "ret"                                     \n\t"\
^

libavcodec/x86/cabac.h:193:9: error: inline assembly requires more registers than available
libavcodec/x86/cabac.h:143:9: note: expanded from macro 'BRANCHLESS_GET_CABAC'

"movzbl "statep"    , "ret"                                     \n\t"\
^

libavcodec/x86/cabac.h:193:9: error: inline assembly requires more registers than available
libavcodec/x86/cabac.h:143:9: note: expanded from macro 'BRANCHLESS_GET_CABAC'

"movzbl "statep"    , "ret"                                     \n\t"\
^

libavcodec/x86/cabac.h:193:9: error: inline assembly requires more registers than available
libavcodec/x86/cabac.h:143:9: note: expanded from macro 'BRANCHLESS_GET_CABAC'

"movzbl "statep"    , "ret"                                     \n\t"\
^

libavcodec/x86/cabac.h:193:9: error: inline assembly requires more registers than available
libavcodec/x86/cabac.h:143:9: note: expanded from macro 'BRANCHLESS_GET_CABAC'

"movzbl "statep"    , "ret"                                     \n\t"\
^

libavcodec/x86/cabac.h:193:9: error: inline assembly requires more registers than available
libavcodec/x86/cabac.h:143:9: note: expanded from macro 'BRANCHLESS_GET_CABAC'

"movzbl "statep"    , "ret"                                     \n\t"\
^

libavcodec/x86/cabac.h:193:9: error: inline assembly requires more registers than available
libavcodec/x86/cabac.h:143:9: note: expanded from macro 'BRANCHLESS_GET_CABAC'

"movzbl "statep"    , "ret"                                     \n\t"\
^

libavcodec/x86/cabac.h:193:9: error: inline assembly requires more registers than available
libavcodec/x86/cabac.h:143:9: note: expanded from macro 'BRANCHLESS_GET_CABAC'

"movzbl "statep"    , "ret"                                     \n\t"\
^