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-inl.h b/compiler/dex/quick/mir_to_lir-inl.h
index 144790e..280dbbe 100644
--- a/compiler/dex/quick/mir_to_lir-inl.h
+++ b/compiler/dex/quick/mir_to_lir-inl.h
@@ -19,7 +19,8 @@
 
 #include "mir_to_lir.h"
 
-#include "dex/compiler_internals.h"
+#include "base/logging.h"
+#include "dex/compiler_ir.h"
 
 namespace art {