port neon to arm64. the register names have changes from r0 to w0 or x0 depending on size.  Passing them as parameters (e.g. %0) makes the code register name agnostic.
BUG=333
TESTED=32 bit build still works.
R=nfullagar@chromium.org

Review URL: https://webrtc-codereview.appspot.com/20669005

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1016 16f28f9a-4ce2-e073-06de-1de4eb20be90