drm/amd/display: Check link_active instead of lane_settings != unknown

[Why]
enable_link_dp_mst checks that cur_link_settings != unknown to determine
that the link is already enabled, to skip redundant enablement calls for
multiple streams on the same link. During dc_reinitialize_hardware,
cur_link_settings on previously-active links is not cleared, which blocks
MST links from being re-enabled after a reinitialization.

[How]
 - check for link_status->link_active instead, as it's the real intent
 - clear cur_link_settings when we clear link_active

Signed-off-by: Joshua Aberback <joshua.aberback@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc_link.c

@@ -1738,7 +1738,7 @@ static enum dc_status enable_link_dp_mst(
 	/* sink signal type after MST branch is MST. Multiple MST sinks
 	 * share one link. Link DP PHY is enable or training only once.
 	 */
-	if (link->cur_link_settings.lane_count != LANE_COUNT_UNKNOWN)
+	if (link->link_status.link_active)
 		return DC_OK;
 
 	/* clear payload table */

drivers/gpu/drm/amd/display/dc/dce110/dce110_hw_sequencer.c

@@ -1530,6 +1530,8 @@ static void power_down_encoders(struct dc *dc)
 				dc->links[i]->link_enc, signal);
 
 		dc->links[i]->link_status.link_active = false;
+		memset(&dc->links[i]->cur_link_settings, 0,
+				sizeof(dc->links[i]->cur_link_settings));
 	}
 }