drm/shmobile: Add run-time dependencies

The shmobile DRM driver is only useful on SuperH and shmobile unless
build testing. I am dropping the SuperH dependencies though because
the driver doesn't even build there, so in practice it is an arm-only
driver for now.
Signed-off-by: NJean Delvare <jdelvare@suse.de>
Acked-by: NLaurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>

drivers/gpu/drm/shmobile/Kconfig

 config DRM_SHMOBILE
 	tristate "DRM Support for SH Mobile"
-	depends on DRM && (ARM || SUPERH)
+	depends on DRM && ARM
+	depends on ARCH_SHMOBILE || COMPILE_TEST
 	select BACKLIGHT_CLASS_DEVICE
 	select DRM_KMS_HELPER
 	select DRM_KMS_FB_HELPER