qdev: add class_init to DeviceInfo

Since we are still dynamically creating TypeInfo, we need to chain the
class_init function in order to be able to make use of it within subclasses of
TYPE_DEVICE.

This will disappear once we register TypeInfos directly.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

hw/qdev.h

@@ -231,6 +231,11 @@ struct DeviceInfo {
     /* device state */
     const VMStateDescription *vmsd;
 
+    /**
+     * See #TypeInfo::class_init()
+     */
+    void (*class_init)(ObjectClass *klass, void *data);
+
     /* Private to qdev / bus.  */
     qdev_initfn init;
     qdev_event unplug;