Implement register allocator for floating point registers.

Also:
- Fix misuses of emitting the rex prefix in the x86_64 assembler.
- Fix movaps code generation in the x86_64 assembler.

Change-Id: Ib6dcf6e7c4a9c43368cfc46b02ba50f69ae69cbe
diff --git a/runtime/stack_map.h b/runtime/stack_map.h
index 9b49d31..b1c46a9 100644
--- a/runtime/stack_map.h
+++ b/runtime/stack_map.h
@@ -88,6 +88,7 @@
     kNone,
     kInStack,
     kInRegister,
+    kInFpuRegister,
     kConstant
   };