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/utils.h b/include/lib/utils.h
index 0936cbb..a234e3c 100644
--- a/include/lib/utils.h
+++ b/include/lib/utils.h
@@ -38,6 +38,8 @@
 #define IS_POWER_OF_TWO(x)			\
 	(((x) & ((x) - 1)) == 0)
 
+#define SIZE_FROM_LOG2_WORDS(n)		(4 << (n))
+
 /*
  * The round_up() macro rounds up a value to the given boundary in a
  * type-agnostic yet type-safe manner. The boundary must be a power of two.