bdk: minerva: prep for ATF direct boot support

bdk/utils/sprintf.h

@@ -17,6 +17,8 @@
 #ifndef _SPRINTF_H_
 #define _SPRINTF_H_
 
+#include <stdarg.h>
+
 #include <utils/types.h>
 
 void s_printf(char *out_buf, const char *fmt, ...);