coresight: Do not scan for graph if none is present

If a graph node is not found for a given node, of_get_next_endpoint()
will emit the following error message :

 OF: graph: no port node found in /<node_name>

If the given component doesn't have any explicit connections (e.g,
ETE) we could simply ignore the graph parsing. As for any legacy
component where this is mandatory, the device will not be usable
as before this patch. Updating the DT bindings to Yaml and enabling
the schema checks can detect such issues with the DT.

Cc: Mike Leach <mike.leach@linaro.org>
Cc: Leo Yan <leo.yan@linaro.org>
Signed-off-by: NSuzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20210405164307.1720226-11-suzuki.poulose@arm.comSigned-off-by: NMathieu Poirier <mathieu.poirier@linaro.org>

drivers/hwtracing/coresight/coresight-platform.c

@@ -90,6 +90,12 @@ static void of_coresight_get_ports_legacy(const struct device_node *node,
 	struct of_endpoint endpoint;
 	int in = 0, out = 0;
 
+	/*
+	 * Avoid warnings in of_graph_get_next_endpoint()
+	 * if the device doesn't have any graph connections
+	 */
+	if (!of_graph_is_present(node))
+		return;
 	do {
 		ep = of_graph_get_next_endpoint(node, ep);
 		if (!ep)