thunderbolt: Add support for XDomain connections

Two domains (hosts) can be connected through a Thunderbolt cable and in
that case they can start software services such as networking over the
high-speed DMA paths. Now that we have all the basic building blocks in
place to create DMA tunnels over the Thunderbolt fabric we can add this
support to the software connection manager as well.

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