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/drivers/gpu/drm/omapdrm/omap_drv.c b/drivers/gpu/drm/omapdrm/omap_drv.c
index 079c54c..902074b 100644
--- a/drivers/gpu/drm/omapdrm/omap_drv.c
+++ b/drivers/gpu/drm/omapdrm/omap_drv.c
@@ -548,6 +548,9 @@
 
 static int pdev_probe(struct platform_device *device)
 {
+	if (omapdss_is_initialized() == false)
+		return -EPROBE_DEFER;
+
 	DBG("%s", device->name);
 	return drm_platform_init(&omap_drm_driver, device);
 }