thunderbolt: Add polling mode for rings

In order to support things like networking over Thunderbolt cable, there
needs to be a way to switch the ring to a mode where it can be polled
with the interrupt masked. We implement such mode so that the caller can
allocate a ring by passing pointer to a function that is then called
when an interrupt is triggered. Completed frames can be fetched using
tb_ring_poll() and the interrupt can be re-enabled when the caller is
finished with polling by using tb_ring_poll_complete().

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Michael Jamet <michael.jamet@intel.com>
Reviewed-by: Yehezkel Bernat <yehezkel.bernat@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>