SIMD pavgb,w for x86/x86_64

Rationale:
Break-out CL of ART Vectorizer.
Enables fast halving add with rounding

Bug: 34083438
Test: assembler_x86[_64]_test
Change-Id: I09173376b803d671a6b05a33e630f45f778cea52
diff --git a/compiler/utils/x86_64/assembler_x86_64.h b/compiler/utils/x86_64/assembler_x86_64.h
index 08e17e8..fc2b117 100644
--- a/compiler/utils/x86_64/assembler_x86_64.h
+++ b/compiler/utils/x86_64/assembler_x86_64.h
@@ -523,6 +523,9 @@
   void orps(XmmRegister dst, XmmRegister src);
   void por(XmmRegister dst, XmmRegister src);
 
+  void pavgb(XmmRegister dst, XmmRegister src);  // no addr variant (for now)
+  void pavgw(XmmRegister dst, XmmRegister src);
+
   void pcmpeqb(XmmRegister dst, XmmRegister src);
   void pcmpeqw(XmmRegister dst, XmmRegister src);
   void pcmpeqd(XmmRegister dst, XmmRegister src);