128 for avx2
128 for avx2

R=harryjin@google.com
BUG=libyuv:461

Review URL: https://webrtc-codereview.appspot.com/55649004.

lemenkov/libyuv,yarrcc/libyuv-ios,lemenkov/libyuv,disigma/yuv,lemenkov/libyuv,yarrcc/libyuv-ios,disigma/yuv,disigma/yuv,yarrcc/libyuv-ios,lemenkov/libyuv,yarrcc/libyuv-ios