Use dbcc_name field from dev_bdi instead of the hole structure in get_hotplug_device_node method
Clean hotplug implementation

* Introducing get_ancestor_session_path which let the consumer get the path
  string to one of it's ancestor devices.
* Implemented parent device filling automatically up to hcd level. In the case
  of hcd levels we resolve the vid and pid from the pci board and put those to
  the hub.
* Correct implementation of hotplug_poll, this method is used for initial
  polling, or every time get_device_list gets called, and refreshes the buses
  if there are any new devices. The way it works now is way simpler than before
  it firsts looks for all usb hubs, which get filled with they're parents hcd
  devices, then it looks for all usb devices which will fill up the tree up to
  the first known parent device, which turns out it's either a hub or a
  composite device.
* Dropping previous code for hotplug polling.