OMAPDSS: add helpers to get mgr or output from display

Add two helper functions that can be used to find either the DSS output
or the overlay manager that is connected to the given display.

This hides how the output and the manager are actually connected, making
it easier to change the connections in the future.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
diff --git a/include/video/omapdss.h b/include/video/omapdss.h
index 25a944e..898f812 100644
--- a/include/video/omapdss.h
+++ b/include/video/omapdss.h
@@ -786,6 +786,9 @@
 		struct omap_dss_device *dssdev);
 int omapdss_output_unset_device(struct omap_dss_output *out);
 
+struct omap_dss_output *omapdss_find_output_from_display(struct omap_dss_device *dssdev);
+struct omap_overlay_manager *omapdss_find_mgr_from_display(struct omap_dss_device *dssdev);
+
 void omapdss_default_get_resolution(struct omap_dss_device *dssdev,
 		u16 *xres, u16 *yres);
 int omapdss_default_get_recommended_bpp(struct omap_dss_device *dssdev);