OMAPDSS: hide manager's enable/disable()

omap_overlay_manager struct contains enable() and disable() functions.
However, these are only meant to be used from inside omapdss, and thus
it's bad to expose the functions.

This patch adds dss_mgr_enable() and dss_mgr_disable() functions to
apply.c, which handle enabling and disabling the output.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
diff --git a/drivers/video/omap2/dss/dsi.c b/drivers/video/omap2/dss/dsi.c
index 101e3b8..9358afa2 100644
--- a/drivers/video/omap2/dss/dsi.c
+++ b/drivers/video/omap2/dss/dsi.c
@@ -4010,7 +4010,7 @@
 	dsi_vc_enable(dsidev, channel, true);
 	dsi_if_enable(dsidev, true);
 
-	dssdev->manager->enable(dssdev->manager);
+	dss_mgr_enable(dssdev->manager);
 
 	return 0;
 }
@@ -4029,7 +4029,7 @@
 	dsi_vc_enable(dsidev, channel, true);
 	dsi_if_enable(dsidev, true);
 
-	dssdev->manager->disable(dssdev->manager);
+	dss_mgr_disable(dssdev->manager);
 }
 EXPORT_SYMBOL(dsi_video_mode_disable);