[app][mdebug] support faster SWO rates, default to 6Mbps

app/mdebug/mdebug.c

@@ -141,7 +141,7 @@ static void mdebug_entry(const struct app_descriptor *app, void *args)
 {
 	udc_start();
 	swo_init(txept);
-	swo_config(1000000);
+	swo_config(6000000);
 
 	for (;;) {
 		if (!online) {

app/mdebug/swo-uart1.c

@@ -130,7 +130,11 @@ void swo_config(unsigned mhz) {
 }
 
 unsigned swo_set_clock(unsigned khz) {
-	if (khz >= 6000) {
+	if (khz >= 12000) {
+		khz = 12000;
+	} else if (khz >= 8000) {
+		khz = 8000;
+	} else if (khz >= 6000) {
 		khz = 6000;
 	} else if (khz >= 4000) {
 		khz = 4000;