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/mir_to_lir.cc b/compiler/dex/quick/mir_to_lir.cc
index 1ff64c9..274e078 100644
--- a/compiler/dex/quick/mir_to_lir.cc
+++ b/compiler/dex/quick/mir_to_lir.cc
@@ -14,10 +14,11 @@
  * limitations under the License.
  */
 
-#include "dex/compiler_internals.h"
+#include "mir_to_lir-inl.h"
+
 #include "dex/dataflow_iterator-inl.h"
 #include "dex/quick/dex_file_method_inliner.h"
-#include "mir_to_lir-inl.h"
+#include "driver/compiler_driver.h"
 #include "primitive.h"
 #include "thread-inl.h"