move BUG_ON, panic and kprintf define to debug.h; add BUILD_BUG_ON

these functions are more logical to keep together there as they depend
on each other.

Also add a comment about the __printf attribute, if we have a quiet
period it would be useful to enable and clear the thousands of
warnings...

Change-Id: I47d3891c9cd87da28b2883c29384959f5abd1459

kernel/include/kmalloc.h

@@ -13,11 +13,9 @@
 #ifndef __HEADER_KMALLOC_H
 #define __HEADER_KMALLOC_H
 
-#include <ihk/mm.h>
-#include <cls.h>
-
-void panic(const char *);
-int kprintf(const char *format, ...);
+#include "ihk/mm.h"
+#include "cls.h"
+#include "debug.h"
 
 #define kmalloc(size, flag) ({\
 void *r = _kmalloc(size, flag, __FILE__, __LINE__);\