drm/amd/display: add flag to allow diag to force enumerate edp

[why]
SLT tests require that diag can drive eDP even if nothing is connected, this is not
typical production use case, so we need to add flag

[how]
add flag, and this flag supercedes "should destroy" logic
Signed-off-by: Jun Lei <Jun.Lei@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -194,7 +194,7 @@ static bool create_links(
 				}
 			}
 
-			if (!should_destory_link) {
+			if (dc->config.force_enum_edp || !should_destory_link) {
 				dc->links[dc->link_count] = link;
 				link->dc = dc;
 				++dc->link_count;

drivers/gpu/drm/amd/display/dc/dc.h

@@ -220,6 +220,7 @@ struct dc_config {
 	bool allow_seamless_boot_optimization;
 	bool power_down_display_on_boot;
 	bool edp_not_connected;
+	bool force_enum_edp;
 	bool forced_clocks;
 	bool disable_extended_timeout_support; // Used to disable extended timeout and lttpr feature as well
 	bool multi_mon_pp_mclk_switch;