64-bit CPUs always have SSE2, and a SSE2 version exists, thus the MMX version will never be used.
This moves all VP3-specific function pointers from dsputil to a new vp3dsp context. There is no reason to ever use the VP3 IDCT where an MPEG2 IDCT is expected or vice versa. Signed-off-by: Mans Rullgard <mans@mansr.com>