superio/smsc/lpc47m10x: Use link-time symbols over .c inclusion

Change-Id: I4a3639c05231eacd016ec3873330f9844befd448
Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-on: http://review.coreboot.org/8080
Tested-by: build bot (Jenkins)
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
diff --git a/src/mainboard/aopen/dxplplusu/romstage.c b/src/mainboard/aopen/dxplplusu/romstage.c
index 86470b3..8bb179a 100644
--- a/src/mainboard/aopen/dxplplusu/romstage.c
+++ b/src/mainboard/aopen/dxplplusu/romstage.c
@@ -29,8 +29,7 @@
 #include "northbridge/intel/e7505/raminit.h"
 
 #include <device/pnp_def.h>
-#include "superio/smsc/lpc47m10x/early_serial.c"
-
+#include <superio/smsc/lpc47m10x/lpc47m10x.h>
 
 #define SERIAL_DEV PNP_DEV(0x2e, LPC47M10X2_SP1)