This basically lets the latest 2.5 ehci-hcd driver compile
in a 2.4 kernel by slightly enriching the API exposed
by usbcore:

    - Some symbols were renamed; in 2.4 transitional APIs,
      drivers can prefer these #defines to the older symbols:
        * URB_SHORT_NOT_OK ... use instead of USB_DISABLE_SPD
        * usb_iso_packet_descriptor ... needs "usb_" prefix
    - usb_make_path() support (topological/physical/stable ids)
        * bus->bus_name (provided during hcd init)
        * dev->devpath (save what hub code threw away)
    - bandwidth related symbols out of <linux/usb.h>
        * they're only provided for hcds
        * exported/updated usb_calc_bandwidth()
    - some stuff that only hcd drivers will care about
        * internal symbols (and urb->*_dma, internal until 2.5)
        * remove pci latency bogosity

Note that the 2.5 HCDs won't yet _work_ yet if anyone brings
them back to 2.4 (note the FIXMEs in this patch, and there's
a bit more).  But this a big step towards making it possible
to have the same (host controller) drivers running on both
kernels, and can help some of other usb device drivers too.

Please merge to Marcelo's tree.  I don't know if I'll have
the ehci driver update ready before pre6 starts to slush.

- Dave