monitor: Use traditional command interface for HMP device_add

All QMP commands use the "new" handler interface (mhandler.cmd_new).
Most HMP commands still use the traditional interface (mhandler.cmd),
but a few use the "new" one.  Complicates handle_user_command() for no
gain, so I'm converting these to the traditional interface.

For device_add, that's easy: just wrap the obvious hmp_device_add()
around do_device_add().

monitor_user_noop() is now unused, drop it.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Luiz Capitulino <lcapitulino@redhat.com>
diff --git a/hmp.c b/hmp.c
index 5a43f9d..514f22f 100644
--- a/hmp.c
+++ b/hmp.c
@@ -22,6 +22,7 @@
 #include "qmp-commands.h"
 #include "qemu/sockets.h"
 #include "monitor/monitor.h"
+#include "monitor/qdev.h"
 #include "qapi/opts-visitor.h"
 #include "qapi/string-output-visitor.h"
 #include "qapi-visit.h"
@@ -1499,6 +1500,11 @@
     }
 }
 
+void hmp_device_add(Monitor *mon, const QDict *qdict)
+{
+    do_device_add(mon, qdict, NULL);
+}
+
 void hmp_device_del(Monitor *mon, const QDict *qdict)
 {
     const char *id = qdict_get_str(qdict, "id");