This patch cleans up some messy parts of this driver, and
was pleasantly painless.

      - gets rid of ED dma hashtables
         * less memory needed
         * also less (+faster) code
         * ... rewrites all ED scheduling ops, they now use
           cpu addresses, like EHCI and UHCI do already

      - simplifies ED scheduling (no dma hashtables)
         * control and bulk lists are now doubly linked
         * periodic tree still singly linked; driver uses a
           new CPU view "shadow" of the hardware framelist
         * previous periodic code was cryptic, almost read-only
         * simpler tree code for EDs with {branch,period}

      - bugfixes periodic scheduling
         * when CONFIG_USB_BANDWIDTH, checks per-frame load
           against the limit; no more dodgey accounting
         * handles iso period != 1; interrupt and iso schedule
           EDs with the same routine (HW sees special TDs)
         * credit usbfs with bandwidth for endpoints, not URBs

      - adds driverfs output (when CONFIG_USB_DEBUG)
         * resembles EHCI:  'async' (control+bulk) and
           'periodic' (interrupt+iso) files show schedules
         * shows only queue heads (EDs) just now (*)

      - has minor text and code cleanups, etc

Now that this logic has morphed into more comprehensible
form, I know what to borrow into the EHCI code!


     (*) It shows TDs on the td_list, but this patch won't
         put them there.  A queue fault handling update will.