southbridge/intel: Tidy up preprocessor and headers

Change-Id: I52a7b39566acd64ac21a345046675e05649a40f5
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34980
Reviewed-by: Furquan Shaikh <furquan@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/southbridge/intel/lynxpoint/serialio.c

@@ -22,6 +22,7 @@
 #include <device/pci.h>
 #include <device/pci_ids.h>
 #include <stdlib.h>
+#include "chip.h"
 #include "pch.h"
 #include "nvs.h"