thunderbolt: Add MSI-X support

Intel Thunderbolt controllers support up to 16 MSI-X vectors. Using
MSI-X is preferred over MSI or legacy interrupt and may bring additional
performance because there is no need to check the status registers which
interrupt was triggered.

While there we convert comments in structs tb_ring and tb_nhi to follow
kernel-doc format more closely.

This code is based on the work done by Amir Levy and Michael Jamet.

Signed-off-by: Michael Jamet <michael.jamet@intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Yehezkel Bernat <yehezkel.bernat@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Andreas Noever <andreas.noever@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>