drm/amd/display: Fallback to dmcub for psr when dmcu is disabled

[Why]
We want to be able to enable/disable psr on dmcub and fallback to dmcu
when necessary.

[How]
Use dc config option to do so.
Signed-off-by: Wyatt Wood <wyatt.wood@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn21/dcn21_resource.c

@@ -1864,7 +1864,7 @@ static bool dcn21_resource_construct(
 		goto create_fail;
 	}
 
-	if (dc->config.psr_on_dmub) {
+	if (dc->debug.disable_dmcu) {
 		pool->base.psr = dmub_psr_create(ctx);
 
 		if (pool->base.psr == NULL) {