USB: xhci: Support interrupt transfers.

Interrupt transfers are submitted to the xHCI hardware using the same TRB
type as bulk transfers.  Re-use the bulk transfer enqueueing code to
enqueue interrupt transfers.

Interrupt transfers are a bit different than bulk transfers.  When the
interrupt endpoint is to be serviced, the xHC will consume (at most) one
TD.  A TD (comprised of sg list entries) can take several service
intervals to transmit.  The important thing for device drivers to note is
that if they use the scatter gather interface to submit interrupt
requests, they will not get data sent from two different scatter gather
lists in the same service interval.

For now, the xHCI driver will use the service interval from the endpoint's
descriptor (bInterval).  Drivers will need a hook to poll at a more
frequent interval.  Set urb->interval to the interval that the xHCI
hardware will use.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>