qmp: add DEVICE_TRAY_MOVED event

It's emitted whenever the tray is moved by the guest or by HMP/QMP
commands.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Acked-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/monitor.h b/monitor.h
index b72ea07..b6f700f 100644
--- a/monitor.h
+++ b/monitor.h
@@ -38,6 +38,7 @@
     QEVENT_SPICE_DISCONNECTED,
     QEVENT_BLOCK_JOB_COMPLETED,
     QEVENT_BLOCK_JOB_CANCELLED,
+    QEVENT_DEVICE_TRAY_MOVED,
     QEVENT_MAX,
 } MonitorEvent;