vorbisdsp: convert x86 simd functions from inline asm to yasm.
floatdsp: move vector_fmul_add from dsputil to avfloatdsp.
floatdsp: move vector_fmul_reverse from dsputil to avfloatdsp.

Now, nellymoserenc and aacenc no longer depends on dsputil. Independent
of this patch, wmaprodec also does not depend on dsputil, so I removed
it from there also.
floatdsp: move butterflies_float from dsputil to avfloatdsp.

This makes wmadec/enc, twinvq and mpegaudiodec (i.e. mp2/mp3)
independent of dsputil.
floatdsp: move scalarproduct_float from dsputil to avfloatdsp.

This makes the aac decoder and all voice codecs independent of dsputil.
dsputil: remove avg_no_rnd_pixels8.

This is never used.
dsputil: remove some never-assigned function pointers from the struct.