drm/amd/display: Disallow entering PSR when panel is disconnected

[WHY]
The dGPU cannot enter PSR when it is not connected to a panel.

[HOW]
Added a check to dc_link_set_psr_allow_active
which returns early if panel is disconnected.
Reviewed-by: Harry Vanzylldejong <harry.vanzylldejong@amd.com>
Reviewed-by: Evgenii Krasnikov <Evgenii.Krasnikov@amd.com>
Reviewed-by: Nicholas Choi <Nicholas.Choi@amd.com>
Acked-by: Pavle Kotarac <Pavle.Kotarac@amd.com>
Signed-off-by: Max Erenberg <merenber@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -3079,6 +3079,11 @@ bool dc_link_set_psr_allow_active(struct dc_link *link, const bool *allow_active
 	if (!dc_get_edp_link_panel_inst(dc, link, &panel_inst))
 		return false;
 
+	if (allow_active && link->type == dc_connection_none) {
+		// Don't enter PSR if panel is not connected
+		return false;
+	}
+
 	/* Set power optimization flag */
 	if (power_opts && link->psr_settings.psr_power_opt != *power_opts) {
 		link->psr_settings.psr_power_opt = *power_opts;