Revert "remove vp9_diamond_search_sad_avx.c"
This reverts commit be12fefa and commit 057c1c40. Also, the mismatch between the avx version and the c version has been fixed. BUG=https://bugs.chromium.org/p/webm/issues/detail?id=1168 For a rt encode using 1080p@60fps material, up to 11% performance improvement overall was seen. Change-Id: Icd1f216209ebc6fc0b8da885f32f356fa4355ed0