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
diff --git a/gyp/common_conditions.gypi b/gyp/common_conditions.gypi
index 0c004e5..d00fe4b 100644
--- a/gyp/common_conditions.gypi
+++ b/gyp/common_conditions.gypi
@@ -263,6 +263,9 @@
                     'cflags': [
                       '-mdspr2',
                     ],
+                    'defines': [
+                      '__MIPS_HAVE_DSPR2',
+                    ],
                   }],
                 ],
               }],