acpi, pc: Add unplug cb for pc machine.

Memory and CPU hot unplug are both asynchronous procedures.
When the unplug operation happens, unplug request cb is called first.
And when guest OS finished handling unplug, unplug cb will be called
to do the real removal of device.

This patch adds hotunplug cb to pc machine, which memory and CPU
hot unplug will use it.
Reviewed-by: NIgor Mammedov <imammedo@redhat.com>
Signed-off-by: NTang Chen <tangchen@cn.fujitsu.com>
Signed-off-by: NZhu Guihua <zhugh.fnst@cn.fujitsu.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/i386/pc.c

@@ -1686,6 +1686,13 @@ static void pc_machine_device_unplug_request_cb(HotplugHandler *hotplug_dev,
                " type: %s", object_get_typename(OBJECT(dev)));
 }
 
+static void pc_machine_device_unplug_cb(HotplugHandler *hotplug_dev,
+                                        DeviceState *dev, Error **errp)
+{
+    error_setg(errp, "acpi: device unplug for not supported device"
+               " type: %s", object_get_typename(OBJECT(dev)));
+}
+
 static HotplugHandler *pc_get_hotpug_handler(MachineState *machine,
                                              DeviceState *dev)
 {
@@ -1816,6 +1823,7 @@ static void pc_machine_class_init(ObjectClass *oc, void *data)
     mc->get_hotplug_handler = pc_get_hotpug_handler;
     hc->plug = pc_machine_device_plug_cb;
     hc->unplug_request = pc_machine_device_unplug_request_cb;
+    hc->unplug = pc_machine_device_unplug_cb;
 }
 
 static const TypeInfo pc_machine_info = {