mb/lenovo/t400/Makefile: Build gpio w/o subdir makefiles

Change-Id: Ia2e889fe72d746b71d92026e358c7471f56b381f
Signed-off-by: Peter Lemenkov <lemenkov@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37287
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/mainboard/lenovo/t400/Makefile.inc

@@ -16,7 +16,7 @@
 bootblock-y += bootblock.c
 bootblock-y += dock.c
 
-subdirs-y += variants/$(VARIANT_DIR)/
+romstage-y += variants/$(VARIANT_DIR)/gpio.c
 
 ramstage-y += dock.c
 ramstage-y += cstates.c

src/mainboard/lenovo/t400/variants/r500/Makefile.inc

@@ -1 +0,0 @@
-romstage-y += gpio.c

src/mainboard/lenovo/t400/variants/t400/Makefile.inc

@@ -1 +0,0 @@
-romstage-y += gpio.c