ART: Refactor GraphVisualizer attribute printing

This patch unifies the way GraphVisualizer prints instruction
attributes in preparation of changes to the Checker syntax.

Change-Id: I44e91e36c660985ddfe039a9f410fedc48b496ec
diff --git a/compiler/optimizing/code_generator_arm.cc b/compiler/optimizing/code_generator_arm.cc
index f56e446..93d0e5b 100644
--- a/compiler/optimizing/code_generator_arm.cc
+++ b/compiler/optimizing/code_generator_arm.cc
@@ -347,11 +347,11 @@
 }
 
 void CodeGeneratorARM::DumpCoreRegister(std::ostream& stream, int reg) const {
-  stream << ArmManagedRegister::FromCoreRegister(Register(reg));
+  stream << Register(reg);
 }
 
 void CodeGeneratorARM::DumpFloatingPointRegister(std::ostream& stream, int reg) const {
-  stream << ArmManagedRegister::FromSRegister(SRegister(reg));
+  stream << SRegister(reg);
 }
 
 size_t CodeGeneratorARM::SaveCoreRegister(size_t stack_index, uint32_t reg_id) {