drm/amd/display: add dmcub support check

[Why & How]
For DCN harvest case, if there is no dmcub support, we should return false
to avoid bugcheck later.

Reviewed-by: Aric Cyr <aric.cyr@amd.com>
Signed-off-by: Jerry Zuo <jerry.zuo@amd.com>
Signed-off-by: Fudongwang <fudong.wang@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

@@ -5574,6 +5574,9 @@ void dc_mclk_switch_using_fw_based_vblank_stretch_shut_down(struct dc *dc)
  */
 bool dc_is_dmub_outbox_supported(struct dc *dc)
 {
+	if (!dc->caps.dmcub_support)
+		return false;
+
 	switch (dc->ctx->asic_id.chip_family) {
 
 	case FAMILY_YELLOW_CARP: