USB: add urb->ep

This patch (as943) prepares the way for eliminating urb->pipe by
introducing an endpoint pointer into struct urb.  For now urb->ep
is set by usb_submit_urb() from the pipe value; eventually drivers
will set it themselves and we will remove urb->pipe completely.

The patch also adds new inline routines to retrieve an endpoint
descriptor's number and transfer type, essentially as replacements for
usb_pipeendpoint and usb_pipetype.

usb_submit_urb(), usb_hcd_submit_urb(), and usb_hcd_unlink_urb() are
converted to use the new field and new routines.  Other parts of
usbcore will be converted in later patches.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>