ARM32/64 NEON versions of ARGBToRGB565DitherRow_NEON are implemented.

BUG=407
TESTED=libyuvTest.* on ARM32/64 with Android
R=fbarchard@google.com

Change-Id: Ia689170fb39db964392e5e1113801592ab0628bf

Review URL: https://webrtc-codereview.appspot.com/49409004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1335 16f28f9a-4ce2-e073-06de-1de4eb20be90