daala_tx: Add SIMD versions of 4-point DST/FlipDST
daala_tx: Add SIMD versions of 4-point DST/FlipDST

Despite the function pointers used to avoid copying and pasting the
boilerplate code around each transform kernel, the compiler will
inline everything to straightline code, with all SIMD parameters
kept in registers.

Change-Id: I3a89d6499e1972967dcccf397507676ee57ee33b

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