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/dss.h b/drivers/video/omap2/dss/dss.h
index 3713dc6..24326a5 100644
--- a/drivers/video/omap2/dss/dss.h
+++ b/drivers/video/omap2/dss/dss.h
@@ -324,8 +324,8 @@
 
 bool dispc_go_busy(enum omap_channel channel);
 void dispc_go(enum omap_channel channel);
-void dispc_enable_lcd_out(bool enable);
-void dispc_enable_digit_out(bool enable);
+void dispc_enable_channel(enum omap_channel channel, bool enable);
+bool dispc_is_channel_enabled(enum omap_channel channel);
 int dispc_enable_plane(enum omap_plane plane, bool enable);
 void dispc_enable_replication(enum omap_plane plane, bool enable);