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/dpi.c b/drivers/video/omap2/dss/dpi.c
index 976ac23..79c4df3 100644
--- a/drivers/video/omap2/dss/dpi.c
+++ b/drivers/video/omap2/dss/dpi.c
@@ -223,7 +223,7 @@
 
 	mdelay(2);
 
-	dssdev->manager->enable(dssdev->manager);
+	dss_mgr_enable(dssdev->manager);
 
 	return 0;
 
@@ -249,7 +249,7 @@
 
 void omapdss_dpi_display_disable(struct omap_dss_device *dssdev)
 {
-	dssdev->manager->disable(dssdev->manager);
+	dss_mgr_disable(dssdev->manager);
 
 	if (dpi_use_dsi_pll(dssdev)) {
 		dss_select_dispc_clk_source(OMAP_DSS_CLK_SRC_FCK);