daala_tx: Add SIMD version of the 4-point DCT
daala_tx: Add SIMD version of the 4-point DCT

Currently this only requires SSSE3 operations, but we build it as
AVX2 to get support for 3-operand instructions. Separate versions
for different instruction sets will be added later.

Change-Id: Ib02c1496832923ecf6dccc1a208dc5ac5559dad2

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom