stdlib: add ALIGN_UP and ALIGN_DOWN macros

There wasn't an equivalent to align down so add ALIGN_DOWN.
For symmetry provide an ALIGN_UP macro as well.

Change-Id: I7033109311eeb15c8c69c649878785378790feb9
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/2951
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/include/stdlib.h

@@ -7,6 +7,8 @@
 
 #define ALIGN(x,a)              __ALIGN_MASK(x,(typeof(x))(a)-1UL)
 #define __ALIGN_MASK(x,mask)    (((x)+(mask))&~(mask))
+#define ALIGN_UP(x,a)           ALIGN((x),(a))
+#define ALIGN_DOWN(x,a)         ((x) & ~((typeof(x))(a)-1UL))
 
 #define MIN(a,b) ((a) < (b) ? (a) : (b))
 #define MAX(a,b) ((a) > (b) ? (a) : (b))