thunderbolt: Store Thunderbolt generation in the switch structure

In some cases it is useful to know what is the Thunderbolt generation
the switch supports. This introduces a new field to struct switch that
stores the generation of the switch based on the device ID. Unknown
switches (there should be none) are assumed to be first generation to be
on the safe side.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Yehezkel Bernat <yehezkel.bernat@intel.com>
Reviewed-by: Michael Jamet <michael.jamet@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>