OMAPDSS: add dispc_ovl_enabled()

Add new dispc function, dispc_ovl_enabled(). This returns if the overlay
enable bit is set in the registers.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/video/omap2/dss/dss.h

@@ -427,6 +427,7 @@ int dispc_ovl_setup(enum omap_plane plane, const struct omap_overlay_info *oi,
 		bool replication, const struct omap_video_timings *mgr_timings,
 		bool mem_to_mem);
 int dispc_ovl_enable(enum omap_plane plane, bool enable);
+bool dispc_ovl_enabled(enum omap_plane plane);
 void dispc_ovl_set_channel_out(enum omap_plane plane,
 		enum omap_channel channel);