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/dex/mir_graph.h b/compiler/dex/mir_graph.h
index 2174f67..d344055 100644
--- a/compiler/dex/mir_graph.h
+++ b/compiler/dex/mir_graph.h
@@ -20,7 +20,7 @@
 #include "dex_file.h"
 #include "dex_instruction.h"
 #include "compiler_ir.h"
-#include "arena_bit_vector.h"
+#include "utils/arena_bit_vector.h"
 #include "utils/growable_array.h"
 
 namespace art {