x86: hevc: adding transform_add

8bits
wo assembly:
- 1753 decicycles in transform add, 975751 runs, 72825 skips
SSE2:
- 490 decicycles in transform add, 1048545 runs, 31 skips


10bits
wo assembly:
- 3534 decicycles in transform add, 1046294 runs, 2282 skips
SSE2:
- 527 decicycles in transform add, 1048525 runs, 51 skips
AVX:
- 483 decicycles in transform add, 1048542 runs, 34 skips
AVX2:
- 338 decicycles in transform add, 1048558 runs, 18 skips