BGR variation of 10 bit conversion using swapped U and V
and mirrored matrix to produce AB30 format instead of AR30.

Bug: libyuv:777
Test: LibYUVConvertTest.H010ToAB30_Opt
Change-Id: I96d115a5d1e12138f40cb548871e03aa3ab210eb
Reviewed-on: https://chromium-review.googlesource.com/922284
Commit-Queue: Frank Barchard <fbarchard@chromium.org>
Reviewed-by: Miguel Casas <mcasas@chromium.org>