drm/amd/display: prevent seamless boot on displays that don't have the preferred dig

Seamless boot requires VBIOS to select dig matching to link order wise. A significant
amount of dal logic makes assumption we are using preferred dig for eDP and if this
isn't the case then seamless boot is not supported.
Reviewed-by: Martin Leung <Martin.Leung@amd.com>
Acked-by: Stylon Wang <stylon.wang@amd.com>
Signed-off-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -1556,6 +1556,9 @@ bool dc_validate_boot_timing(const struct dc *dc,
 	if (tg_inst >= dc->res_pool->timing_generator_count)
 		return false;
 
+	if (tg_inst != link->link_enc->preferred_engine)
+		return false;
+
 	tg = dc->res_pool->timing_generators[tg_inst];
 
 	if (!tg->funcs->get_hw_timing)