MIPS: added optimization for functions from SkBlitRow.

gain is ~40%

following function are optimized:
  S32_D565_Blend
  S32A_D565_Opaque_Dither
  S32_D565_Opaque_Dither
  S32_D565_Blend_Dither
  S32A_D565_Opaque
  S32A_D565_Blend
  S32_Blend_BlitRow32

R=djsollen@google.com, teodora.petrovic@gmail.com

Author: djordje.pesut@imgtec.com

Review URL: https://codereview.chromium.org/326913004
3 files changed