Rename OpCode.h -> DexOpcodes.h.

Also incorporate the former contents of OpCodeNames.h. This is a small
attempt to increase naming consistency in libdex. There will be a bit
more to come, in a follow-up.

Change-Id: Ia7ab06042dde2e19eda02ef1fee72fb4260e899d
diff --git a/vm/compiler/codegen/arm/ArchUtility.c b/vm/compiler/codegen/arm/ArchUtility.c
index 2e68459..7649300 100644
--- a/vm/compiler/codegen/arm/ArchUtility.c
+++ b/vm/compiler/codegen/arm/ArchUtility.c
@@ -15,7 +15,7 @@
  */
 
 #include "../../CompilerInternals.h"
-#include "libdex/OpCodeNames.h"
+#include "libdex/DexOpcodes.h"
 #include "ArmLIR.h"
 
 static char *shiftNames[4] = {