include: Move snprintf to stdio.h

Move snprintf to stdio.h since it is needed by exteranl libraries.

Signed-off-by: Raymond Mao <raymond.mao@linaro.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

lib/vsprintf.c

@@ -19,6 +19,7 @@
 #include <hexdump.h>
 #include <stdarg.h>
 #include <uuid.h>
+#include <stdio.h>
 #include <vsprintf.h>
 #include <linux/ctype.h>
 #include <linux/err.h>