VeNum optimizations to libpng to improve PNG decode time

Set correct counter in neon routine for SUB filter type.
Enable Neon optimizations for all filter types and pixel depths.
cherry picked from commit b912f64bc4bb174fc055cda58e303faaa640b8b1

Change-Id: I296bfd2046f18f93b54a71cf86aef19a7fab2de1