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>

src/superio/smsc/sio1036/superio.c

@@ -18,7 +18,6 @@
 #include <device/device.h>
 #include <device/pnp.h>
 #include <superio/conf_mode.h>
-#include <stdlib.h>
 
 #include "sio1036.h"