ART: Some Quick cleanup

Make several fields const in CompilationUnit. May benefit some Mir2Lir
code that repeats tests, and in general immutability is good.

Remove compiler_internals.h and refactor some other headers to reduce
overly broad imports (and thus forced recompiles on changes).

Change-Id: I898405907c68923581373b5981d8a85d2e5d185a
diff --git a/compiler/dex/ssa_transformation.cc b/compiler/dex/ssa_transformation.cc
index 3905649..6bd49de 100644
--- a/compiler/dex/ssa_transformation.cc
+++ b/compiler/dex/ssa_transformation.cc
@@ -15,7 +15,8 @@
  */
 
 #include "base/bit_vector-inl.h"
-#include "compiler_internals.h"
+#include "base/logging.h"
+#include "compiler_ir.h"
 #include "dataflow_iterator-inl.h"
 #include "utils/scoped_arena_containers.h"