Adds subract, move wide immediate instructions to ARM64.

runtime/vm/constants_arm64.h

Index: runtime/vm/constants_arm64.h
===================================================================
--- runtime/vm/constants_arm64.h	(revision 34712)
+++ runtime/vm/constants_arm64.h	(working copy)
@@ -281,7 +281,7 @@
 
 // C3.5.1
 enum AddSubShiftExtOp {
-  AddSubShiftExtMask = 0x1f200000,
+  AddSubShiftExtMask = 0x1f000000,
   AddSubShiftExtFixed = DPRegisterFixed | B24,
   ADD = AddSubShiftExtFixed,
   SUB = AddSubShiftExtFixed | B30,
@@ -363,6 +363,9 @@
   kImm16Shift = 5,
   kImm16Bits = 16,
 
+  kHWShift = 21,
+  kHWBits = 2,
+
   // Shift and Extend.
   kShiftExtendShift = 21,
   kShiftExtendBits = 1,
@@ -448,6 +451,7 @@
 
   inline int Imm12ShiftField() const {
     return Bits(kImm12ShiftShift, kImm12ShiftBits); }
+  inline int HWField() const { return Bits(kHWShift, kHWBits); }
 
   // Shift and Extend.
   inline bool IsShift() const { return (Bit(kShiftExtendShift) == 0); }