OMAPDSS: Fix crash with DT boot

When booting with DT, there's a crash when omapfb is probed. This is
caused by the fact that omapdss+DT is not yet supported, and thus
omapdss is not probed at all. On the other hand, omapfb is always
probed. When omapfb tries to use omapdss, there's a NULL pointer
dereference crash. The same error should most likely happen with omapdrm
and omap_vout also.

To fix this, add an "initialized" state to omapdss. When omapdss has
been probed, it's marked as initialized. omapfb, omapdrm and omap_vout
check this state when they are probed to see that omapdss is actually
there.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Tested-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
diff --git a/include/video/omapdss.h b/include/video/omapdss.h
index caefa09..9b52340 100644
--- a/include/video/omapdss.h
+++ b/include/video/omapdss.h
@@ -741,6 +741,7 @@
 };
 
 enum omapdss_version omapdss_get_version(void);
+bool omapdss_is_initialized(void);
 
 int omap_dss_register_driver(struct omap_dss_driver *);
 void omap_dss_unregister_driver(struct omap_dss_driver *);