ARM Skia NEON patches - 24 - S32_D565_Blend_Dither slight speedup/bugfix

ARM Skia NEON patches - 24 - S32_D565_Blend_Dither slight speedup/bugfix

BlitRow565: S32_D565_Blend_Dither, slight speedup + bugfix

This patch adds a rewrite of S32_D565_Blend_Dither in intrinsics.
The newer version is faster (10-20% depending on the value of count)
and also supports ARGB as well as ABGR. It also adds the missing
assert at the beginning of the function.

Signed-off-by: Kévin PETIT <kevin.petit@arm.com>
BUG=
R=djsollen@google.com, mtklein@google.com

Author: kevin.petit.arm@gmail.com

Review URL: https://chromiumcodereview.appspot.com/22566002

git-svn-id: http://skia.googlecode.com/svn/trunk@11473 2bbb7eff-a529-9590-31e7-b0007b416f81