thunderbolt: Show link type for XDomain connections too

Following what we do for routers already, extend this to XDomain
connections as well. This will show in sysfs whether the link is in USB4
or Thunderbolt mode.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>