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>
diff --git a/lib/hexdump.c b/lib/hexdump.c
index 33e3e6e..2bc508f 100644
--- a/lib/hexdump.c
+++ b/lib/hexdump.c
@@ -10,7 +10,7 @@
 
 #include <hexdump.h>
 #include <mapmem.h>
-#include <vsprintf.h>
+#include <stdio.h>
 #include <linux/ctype.h>
 #include <linux/compat.h>
 #include <linux/log2.h>