OMAP: DSS2: move enable/disable_channel to overlay manager

Move enable/disable_channel() from omap_dss_device to overlay manager.

This is part of a larger patch-set, which moves the control from omapdss
driver to the display driver.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>
diff --git a/drivers/video/omap2/dss/dsi.c b/drivers/video/omap2/dss/dsi.c
index 82733d1..b478a50 100644
--- a/drivers/video/omap2/dss/dsi.c
+++ b/drivers/video/omap2/dss/dsi.c
@@ -3013,7 +3013,7 @@
 						x, y, w, h);
 
 				dispc_enable_sidle();
-				dispc_enable_lcd_out(0);
+				device->manager->disable(device->manager);
 
 				dsi_reset_tx_fifo(0);
 			} else {