BUG=319
TESTED=libyuv_unittest
R=fbarchard@chromium.org, fbarchard@google.com

Add the following functions:
 - ScaleRowDown34_NEON
 - ScaleRowDown34_0_Box_NEON
 - ScaleRowDown34_1_Box_NEON

Change-Id: If3fe96de602b77033ec67252ef755ef3f88f33aa

Review URL: https://webrtc-codereview.appspot.com/20209004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1070 16f28f9a-4ce2-e073-06de-1de4eb20be90