move ARRAY_SIZE macro to types.h

The ARRAY_SIZE macro was defined in several target files, so move it
to types.h.

This patch also removes two other identical macros: DIM (from jtag.h)
and asizeof (from arm11.h).

src/helper/types.h

@@ -60,6 +60,16 @@ typedef bool _Bool;
 #define __stringify(s) #s
 
 
+/**
+ * Compute the number of elements of a variable length array.
+ * <code>
+ * const char *strs[] = { "a", "b", "c" };
+ * unsigned num_strs = ARRAY_SIZE(strs);
+ * </code>
+ */
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof(*(x)))
+
+
 /**
  * Cast a member of a structure out to the containing structure.
  * @param ptr The pointer to the member.