src: Add missing include <stdlib.h>

Change-Id: I17dc2fed6c6518daf5af286788c98c049088911e
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37366
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>

src/arch/x86/acpi_device.c

@@ -17,6 +17,7 @@
 #include <arch/acpigen.h>
 #include <device/device.h>
 #include <device/path.h>
+#include <stdlib.h>
 #if CONFIG(GENERIC_GPIO_LIB)
 #include <gpio.h>
 #endif