Was SSSE3 I420ToAR30_Opt (635 ms)
Now AVX2  I420ToAR30_Opt (446 ms)

Bug: libyuv:751
Test:  LibYUVConvertTest.H010ToAR30_Opt
Change-Id: I261be19ec981136a8f453ae0d3211532a790e5c5
Reviewed-on: https://chromium-review.googlesource.com/887750Reviewed-by: Frank Barchard <fbarchard@chromium.org>
Reviewed-by: Cheng Wang <wangcheng@google.com>
Commit-Queue: Frank Barchard <fbarchard@chromium.org>