- Added function fidtx4_sse2().
- Turned on vp10_fht4x4_sse2() for these tx types.
- Updated 4x4 unit test for speed/accuracy.
- 4x4 Unit test passed.
- Running 20K times with random numbers for tx type from
  V_DCT to H_FLIPADST, SSE2 against C, speed improves ~46%.

Change-Id: I828088b7f98dc0f5939a72e3fcd6cb0b8d8dd8bf