thunderbolt: Add device links only when software connection manager is used

We only need to set up the device links when software connection manager
path is used. The firmware connection manager does not need them and if
they are present they may even cause problems.

Reviewed-by: Yehezkel Bernat <YehezkelShB@gmail.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Change-Id: If16d72b80b96b3c7ba9a81ae2103612d7f710290