mb/{hp,intel}: Remove unused <stdlib.h>

Change-Id: Ib6151ac245870a198afb71909a36a0840480d567
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/33906
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/mainboard/intel/strago/gpio.c

@@ -16,7 +16,6 @@
 
 #include "irqroute.h"
 #include <soc/gpio.h>
-#include <stdlib.h>
 #include <boardid.h>
 #include "onboard.h"
 #include "gpio.h"