qdev: Add a get_dev_path() function to BusInfo

This function is meant to provide a stable device path for buses
which are able to implement it.  If a bus has a globally unique
addresses scheme, one address level may be sufficient to provide
a path.  Other buses may need to recursively traverse up the
qdev tree.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

hw/qdev.h

diff --git a/hw/qdev.h b/hw/qdev.h
index cbc89f2..3e22eec 100644
--- a/hw/qdev.h
+++ b/hw/qdev.h
@@ -49,10 +49,13 @@
 };
 
 typedef void (*bus_dev_printfn)(Monitor *mon, DeviceState *dev, int indent);
+typedef char *(*bus_get_dev_path)(DeviceState *dev);
+
 struct BusInfo {
     const char *name;
     size_t size;
     bus_dev_printfn print_dev;
+    bus_get_dev_path get_dev_path;
     Property *props;
 };