drm/tilcdc: only build on arm

[airlied: hack for now until we fix cma helpers on other OF platforms]
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Dave Airlie <airlied@linux.ie>

drivers/gpu/drm/tilcdc/Kconfig

 config DRM_TILCDC
 	tristate "DRM Support for TI LCDC Display Controller"
-	depends on DRM && OF
+	depends on DRM && OF && ARM
 	select DRM_KMS_HELPER
 	select DRM_KMS_CMA_HELPER
 	select DRM_GEM_CMA_HELPER