AArch64: fix and enable sparse- and packed-switch.

Changed implementation of sparse- and packed-switch to use w and x
registers appropriately. Also added a couple of utilities to obtain a
w/s register corresponding to a given x/d register and viceversa.

Change-Id: I485a110f6e91b09227d9e2a0b8b14224a10bca90
diff --git a/compiler/dex/frontend.cc b/compiler/dex/frontend.cc
index 547c0f6..a366a20 100644
--- a/compiler/dex/frontend.cc
+++ b/compiler/dex/frontend.cc
@@ -157,6 +157,8 @@
     Instruction::GOTO,
     Instruction::GOTO_16,
     Instruction::GOTO_32,
+    Instruction::PACKED_SWITCH,
+    Instruction::SPARSE_SWITCH,
     Instruction::IF_EQ,
     Instruction::IF_NE,
     Instruction::IF_LT,
@@ -248,8 +250,6 @@
     Instruction::MOVE_OBJECT,
     Instruction::MOVE_OBJECT_FROM16,
     Instruction::MOVE_OBJECT_16,
-    // Instruction::PACKED_SWITCH,
-    // Instruction::SPARSE_SWITCH,
     // Instruction::MOVE_RESULT,
     // Instruction::MOVE_RESULT_WIDE,
     // Instruction::MOVE_RESULT_OBJECT,