This fixes a couple issues I noted when I finally spent some time
looking at the first version of driverfs support for usb:

- "name" fields (really descriptions) aren't very useful.

     * for devices, they always said "USB device 0000:0000"
         --> Now they'll only say that when there's
             nothing better to be said ...
         --> ... and it's really device 0000:0000!  It was
             using device descriptor fields before they were
             fetched from the device.
         --> Uses product and/or manufacturer strings, which
             most devices have, much like PCI uses the PCI ID
             database (when it's compiled in)

     * for interfaces, it was "figure out some name..."
         --> Now it combines the strings used in the
             usb_make_path() call with interface number
         --> Or in the remote chance a device provides
             an interface string, that's preferred.
         --> In general, I think the driver for each
             interface is best suited to describe it;
             I modified the hub driver to do so.

- "bus_id" field

     * For hub ports, it was wasting code: we know the port
       already, no need to search for it.  Plus, it used
       0-index ids not the 1-index ones matching physical
       labels on hubs, and other user-visible diagnostics.

     * For interfaces, it mixed the device address with the
       interface number ... producing unstable IDs that were
       moreover rather cryptic.  Changed:  "if0" now, using
       the interface ID (not index).

     * For busses, left "usb_bus" alone ... :)

- Adds two files exposing current configuration (for devices)
   and altsetting (for interfaces).

- I was getting a useless diagnostic from the hub driver,
   now it's less useless (it fully identifies the hub)