To ensure fast encoding/decoding on devices without ssse3 support,
SSE2 optimization of sub-pixel filters was done. Test using 1080p
clip showed the decoder speeds were ~70fps with ssse3 filters, ~60fps
with sse2 filters, and ~15fps with c filters.

Change-Id: Ie2088f87d83a889fba80a613e4d0e287aadd785c