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

lib/bitmap.c

@@ -11,9 +11,9 @@
 #include <ctype.h>
 #include <limits.h>
 #include <bitmap.h>
+#include <debug.h>
 
 #define EXPORT_SYMBOL(x)
-#define BUG_ON(x)
 
 /**
  * hex_to_bin - convert a hex digit to its real value