Enable ssse3 version of vp9_fdct8x8_quant

It improves the speed performance of vp9_fdct8x8_quant_sse2 by
about 5%.

Change-Id: I74b093ba4d81df64caf71ac7693f3d917f673097
Merge "Enable ssse3 version of vp9_fdct8x8_quant"