drm/amd/display: create a function to decide mst link settings

[why]
create a dedicated function to make mst link settings decision, so that
the policy's decision is made in a unified place.

Signed-off-by: Wenjing Liu <[e-mail]>
Reviewed-by: Tony Cheng <[e-mail]>
Acked-by: Rodrigo Siqueira <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

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

···
 	return false;
 }
 
+static bool decide_mst_link_settings(const struct dc_link *link, struct dc_link_settings *link_setting)
+{
+	*link_setting = link->verified_link_cap;
+	return true;
+}
+
 void decide_link_settings(struct dc_stream_state *stream,
 	struct dc_link_settings *link_setting)
 {
···
 	 * TODO: add MST specific link training routine
 	 */
 	if (stream->signal == SIGNAL_TYPE_DISPLAY_PORT_MST) {
-		*link_setting = link->verified_link_cap;
-		return;
-	}
-
-	if (link->connector_signal == SIGNAL_TYPE_EDP) {
+		if (decide_mst_link_settings(link, link_setting))
+			return;
+	} else if (link->connector_signal == SIGNAL_TYPE_EDP) {
 		if (decide_edp_link_settings(link, link_setting, req_bw))
 			return;
 	} else if (decide_dp_link_settings(link, link_setting, req_bw))