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/quick/gen_loadstore.cc b/compiler/dex/quick/gen_loadstore.cc
index d314601..9f36e35 100644
--- a/compiler/dex/quick/gen_loadstore.cc
+++ b/compiler/dex/quick/gen_loadstore.cc
@@ -14,9 +14,10 @@
  * limitations under the License.
  */
 
+#include "mir_to_lir-inl.h"
+
 #include "dex/compiler_ir.h"
-#include "dex/compiler_internals.h"
-#include "dex/quick/mir_to_lir-inl.h"
+#include "dex/mir_graph.h"
 #include "invoke_type.h"
 
 namespace art {