include/stdlib.h: Extend common macro collection

Add the following useful macros:

 * Absolute Value Macro
 * Taking ceiling of (a / b)
 * Check if value x is a power of 2 or not

Change-Id: I4e9a326aea3cdd963f13548d1fb63331a57d84b1
Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-on: http://review.coreboot.org/6198
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

src/include/stdlib.h

@@ -12,6 +12,9 @@
 
 #define MIN(a,b) ((a) < (b) ? (a) : (b))
 #define MAX(a,b) ((a) > (b) ? (a) : (b))
+#define ABS(a) (((a) < 0) ? (-(a)) : (a))
+#define CEIL_DIV(a, b)  (((a) + (b) - 1) / (b))
+#define IS_POWER_OF_2(x)  (((x) & ((x) - 1)) == 0)
 
 #define min(a,b) MIN((a),(b))
 #define max(a,b) MAX((a),(b))