ART: Refactor bit_utils and stl_util

Move iterator code from bit_utils.h into bit_utils_iterator.h. Move
Identity into stl_util_identity.h. Remove now unnecessary includes,
and fix up transitive users.

Test: m
Change-Id: Id1ce9cda66827c5d00584f39ed310b6b37629906
diff --git a/compiler/optimizing/code_generator.cc b/compiler/optimizing/code_generator.cc
index 1364018..93234f9 100644
--- a/compiler/optimizing/code_generator.cc
+++ b/compiler/optimizing/code_generator.cc
@@ -41,6 +41,8 @@
 #include "code_generator_mips64.h"
 #endif
 
+#include "base/bit_utils.h"
+#include "base/bit_utils_iterator.h"
 #include "bytecode_utils.h"
 #include "class_linker.h"
 #include "compiled_method.h"