drm/i915: Avoid mixing up SST and MST in DDI setup

The MST vs. SST selection should depend purely on the choice of the
connector/encoder. So don't try to determine the correct DDI mode
based on the intel_dp->is_mst, which simply tells us whether the sink
is in MST mode or not. Instead derive the information from the encoder
type. Since the link training code deals in non-fake encoders, we'll
also need to keep a second copy of that information around, which we'll
now designate as 'link_mst'.

Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1469717448-4297-4-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 50cdc89..55af7f0 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -852,6 +852,7 @@
 	int link_rate;
 	uint8_t lane_count;
 	uint8_t sink_count;
+	bool link_mst;
 	bool has_audio;
 	bool detect_done;
 	enum hdmi_force_audio force_audio;