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/test/dm/scmi.c b/test/dm/scmi.c
index 69fc900..c9a0352 100644
--- a/test/dm/scmi.c
+++ b/test/dm/scmi.c
@@ -18,7 +18,7 @@
 #include <scmi_agent.h>
 #include <scmi_agent-uclass.h>
 #include <scmi_protocols.h>
-#include <vsprintf.h>
+#include <stdio.h>
 #include <asm/scmi_test.h>
 #include <dm/device-internal.h>
 #include <dm/test.h>