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/drivers/video/omap2/omapfb/omapfb-main.c b/drivers/video/omap2/omapfb/omapfb-main.c
index 856917b..cc8953c 100644
--- a/drivers/video/omap2/omapfb/omapfb-main.c
+++ b/drivers/video/omap2/omapfb/omapfb-main.c
@@ -2363,18 +2363,16 @@
 	int i, r;
 	struct omap_overlay_manager *mgr;
 
-	if (!def_dssdev->output) {
-		dev_err(fbdev->dev, "no output for the default display\n");
-		return -EINVAL;
-	}
-
 	for (i = 0; i < fbdev->num_displays; ++i) {
 		struct omap_dss_device *dssdev = fbdev->displays[i].dssdev;
-		struct omap_dss_output *out = dssdev->output;
+		struct omap_dss_output *out;
+
+		out = omapdss_find_output_from_display(dssdev);
+		if (!out)
+			continue;
 
 		mgr = omap_dss_get_overlay_manager(out->dispc_channel);
-
-		if (!mgr || !out)
+		if (!mgr)
 			continue;
 
 		if (mgr->output)
@@ -2383,7 +2381,7 @@
 		mgr->set_output(mgr, out);
 	}
 
-	mgr = def_dssdev->output->manager;
+	mgr = omapdss_find_mgr_from_display(def_dssdev);
 
 	if (!mgr) {
 		dev_err(fbdev->dev, "no ovl manager for the default display\n");