Move common static helpers from codegen to the macro-assembler files.

src/x64/codegen-x64.h

Index: src/x64/codegen-x64.h
===================================================================
--- src/x64/codegen-x64.h	(revision 5806)
+++ src/x64/codegen-x64.h	(working copy)
@@ -341,10 +341,6 @@
   bool in_spilled_code() const { return in_spilled_code_; }
   void set_in_spilled_code(bool flag) { in_spilled_code_ = flag; }
 
-  static Operand ContextOperand(Register context, int index) {
-    return Operand(context, Context::SlotOffset(index));
-  }
-
  private:
   // Type of a member function that generates inline code for a native function.
   typedef void (CodeGenerator::*InlineFunctionGenerator)
@@ -417,10 +413,6 @@
                                             JumpTarget* slow);
 
   // Expressions
-  static Operand GlobalObject() {
-    return ContextOperand(rsi, Context::GLOBAL_INDEX);
-  }
-
   void LoadCondition(Expression* x,
                      ControlDestination* destination,
                      bool force_control);