Move arena_bit_vector.h/cc to compiler/utils.

Also move MIR's BasicBlock related code from arena_bit_vector.h to
bit_vector_block_iterator.cc.

Change-Id: I85c224b387d31cf57a1ef1f1a36eaadf22f1c85d
diff --git a/compiler/optimizing/nodes.h b/compiler/optimizing/nodes.h
index 8f6a26c..3d5d531 100644
--- a/compiler/optimizing/nodes.h
+++ b/compiler/optimizing/nodes.h
@@ -18,8 +18,8 @@
 #define ART_COMPILER_OPTIMIZING_NODES_H_
 
 #include "utils/allocation.h"
+#include "utils/arena_bit_vector.h"
 #include "utils/growable_array.h"
-#include "dex/arena_bit_vector.h"
 
 namespace art {