drm/sun4i: support TCONs without channel 1

Some Allwinner SoCs, such as the A33, have a variation of the TCON that
doesn't have a second channel (or it is not wired to anything).

Make sure we can handle that case.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>

drivers/gpu/drm/sun4i/sun4i_tcon.h

@@ -164,6 +164,8 @@ struct sun4i_tcon {
 	bool				has_mux;
 
 	struct drm_panel		*panel;
+
+	bool				has_channel_1;
 };
 
 struct drm_bridge *sun4i_tcon_find_bridge(struct device_node *node);