drm/tilcdc: Force building of DRM_TILCDC_SLAVE_COMPAT

If I read Documentation/kbuild/makefiles.txt section 3.6 right, this
patch should not be needed. However, without this patch the objects
needed for DRM_TILCDC_SLAVE_COMPAT are not linked, if DRM_TILCDC is
built as module.
Signed-off-by: NJyri Sarha <jsarha@ti.com>
Acked-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

drivers/gpu/drm/Makefile

@@ -60,7 +60,7 @@ obj-$(CONFIG_DRM_ATMEL_HLCDC)	+= atmel-hlcdc/
 obj-$(CONFIG_DRM_RCAR_DU) += rcar-du/
 obj-$(CONFIG_DRM_SHMOBILE) +=shmobile/
 obj-$(CONFIG_DRM_OMAP)	+= omapdrm/
-obj-$(CONFIG_DRM_TILCDC)	+= tilcdc/
+obj-y			+= tilcdc/
 obj-$(CONFIG_DRM_QXL) += qxl/
 obj-$(CONFIG_DRM_BOCHS) += bochs/
 obj-$(CONFIG_DRM_MSM) += msm/