qdev hotplug: infrastructure and monitor commands.

Adds device_add and device_del commands.  device_add accepts accepts
the same syntax like the -device command line switch.  device_del
expects a device id.  So you should tag your devices with ids if you
want to remove them later on, like this:

  device_add pci-ohci,id=ohci
  device_del ohci

Unplugging via pci_del or usb_del works too.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/vl.c b/vl.c
index dd2de98..fd1cc01 100644
--- a/vl.c
+++ b/vl.c
@@ -5959,6 +5959,8 @@
         exit(1);
     }
 
+    qdev_machine_creation_done();
+
     if (loadvm) {
         if (load_vmstate(cur_mon, loadvm) < 0) {
             autostart = 0;