vf_mp: Do not build if inline assembly is not available

Rather than modify the mplayer filter sources, just disable
vf_mp if inline assembly is not available.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

configure

@@ -1897,7 +1897,7 @@ frei0r_src_filter_deps="frei0r dlopen"
 frei0r_src_filter_extralibs='$ldl'
 hqdn3d_filter_deps="gpl"
 movie_filter_deps="avcodec avformat"
-mp_filter_deps="gpl avcodec swscale postproc"
+mp_filter_deps="gpl avcodec swscale postproc inline_asm"
 mptestsrc_filter_deps="gpl"
 negate_filter_deps="lut_filter"
 resample_filter_deps="avresample"