stddef.h: Add standard defines for KiB, MiB, GiB, and TiB

Paul points out that some people like 1024*1024, others like
1048576, but in any case these are all open to typos.

Define KiB, MiB, GiB, and TiB as in the standard so people can use them.

Change-Id: Ic1b57e70d3e9b9e1c0242299741f71db91e7cd3f
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: http://review.coreboot.org/2769
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins)

src/include/stddef.h

@@ -13,6 +13,13 @@ typedef unsigned int wint_t;
 
 #define NULL ((void *)0)
 
+/* Standard units. */
+#define KiB (1<<10)
+#define MiB (1<<20)
+#define GiB (1<<30)
+/* Could we ever run into this one? I hope we get this much memory! */
+#define TiB (1<<40)
+
 #define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
 
 #ifdef __PRE_RAM__