SplitUVRow_AVX2 ported to GCC/NaCL. BUG=269 TESTED=validator for nacl. R=harryjin@google.com
SplitUVRow_AVX2 ported to GCC/NaCL.
BUG=269
TESTED=validator for nacl.
R=harryjin@google.com

Review URL: https://webrtc-codereview.appspot.com/28979004
flykickbird/libyuv,flykickbird/libyuv,flykickbird/libyuv