drm/sun4i: tcon: Reduce the scope of the LVDS error a bit

The current logic to deal with old DT missing the LVDS properties doesn't
take into account whether the LVDS output is supported in the first place,
resulting in spurious error messages on SoCs where it doesn't even matter.

Introduce a new TCON flag to list if LVDS is supported at all to prevent
this from happening.

Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180221125703.4595-1-maxime.ripard@bootlin.com
diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.h b/drivers/gpu/drm/sun4i/sun4i_tcon.h
index b761c7b..278700c 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.h
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.h
@@ -175,6 +175,7 @@ struct sun4i_tcon_quirks {
 	bool	has_channel_1;	/* a33 does not have channel 1 */
 	bool	has_lvds_alt;	/* Does the LVDS clock have a parent other than the TCON clock? */
 	bool	needs_de_be_mux; /* sun6i needs mux to select backend */
+	bool	supports_lvds;   /* Does the TCON support an LVDS output? */
 
 	/* callback to handle tcon muxing options */
 	int	(*set_mux)(struct sun4i_tcon *, const struct drm_encoder *);