drm/i915: Allow per-lane drive settings with LTTPRs

LTTPRs should support per-lane drive settings I think, and even if
they don't they should implement their own fallback logic to determine
suitable common drive settings to use for all the lanes.

v2: Actually check the correct thing
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211001130107.1746-11-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/display/intel_dp_link_training.c

@@ -304,7 +304,7 @@ static u8 intel_dp_phy_preemph_max(struct intel_dp *intel_dp,
 static bool has_per_lane_signal_levels(struct intel_dp *intel_dp,
 				       enum drm_dp_phy dp_phy)
 {
-	return false;
+	return !intel_dp_phy_is_downstream_of_source(intel_dp, dp_phy);
 }
 
 static u8 intel_dp_get_lane_adjust_train(struct intel_dp *intel_dp,