src: Use include <delay.h> when appropriate

Change-Id: I23bc0191ca8fcd88364e5c08be7c90195019e399
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/32012
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>
Reviewed-by: David Guckian

src/drivers/aspeed/common/ast_dp501.c

@@ -15,6 +15,8 @@
  * GNU General Public License for more details.
  */
 
+#include <delay.h>
+
 #include "ast_drv.h"
 
 static void send_ack(struct ast_private *ast)