thunderbolt: Find XDomain by route instead of UUID

We are going to represent loops back to the host also as XDomains and
they all have the same (host) UUID, so finding them needs to use route
string instead. This also requires that we check if the XDomain device
is added to the bus before its properties can be updated. Otherwise the
remote UUID might not be populated yet.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Yehezkel Bernat <YehezkelShB@gmail.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>