superio: Use 'include <stdlib.h>' when appropriate

Change-Id: I55e7b680e128f29a9fd549edfb676e6571330677
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/32830
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
diff --git a/src/superio/nuvoton/wpcm450/superio.c b/src/superio/nuvoton/wpcm450/superio.c
index c666818..aeb394a 100644
--- a/src/superio/nuvoton/wpcm450/superio.c
+++ b/src/superio/nuvoton/wpcm450/superio.c
@@ -17,7 +17,7 @@
 #include <device/device.h>
 #include <device/pnp.h>
 #include <pc80/keyboard.h>
-#include <stdlib.h>
+
 #include "wpcm450.h"
 
 static void init(struct device *dev)