Move SIZE_FROM_LOG2_WORDS macro to utils.h

This patch moves the macro SIZE_FROM_LOG2_WORDS() defined in
`arch.h` to `utils.h` as it is utility macro.

Change-Id: Ia8171a226978f053a1ee4037f80142c0a4d21430
diff --git a/include/lib/aarch64/arch.h b/include/lib/aarch64/arch.h
index 07bbd89..fa5cb12 100644
--- a/include/lib/aarch64/arch.h
+++ b/include/lib/aarch64/arch.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2015, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2016, ARM Limited and Contributors. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
@@ -334,8 +334,6 @@
 #define CTR_IMINLINE_MASK	0xf
 
 #define MAX_CACHE_LINE_SIZE	0x800 /* 2KB */
-#define SIZE_FROM_LOG2_WORDS(n)	(4 << (n))
-
 
 /* Physical timer control register bit fields shifts and masks */
 #define CNTP_CTL_ENABLE_SHIFT   0