thunderbolt: Do not tear down tunnels when driver is unloaded

Now that we have capability to discover existing tunnels during driver
load there is no point tearing down tunnels when the driver gets
unloaded. Instead we can just leave them running. If user disconnects
devices while there is no Thunderbolt driver loaded, tunneled protocol
hotplug happens and is handled by the corresponding driver (pciehp in
case of PCIe tunnel, GFX driver in case of DP tunnel).

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>