thunderbolt: Split setting link width and lane bonding into own functions

When bonding lanes over XDomain the host that has "higher" UUID triggers
link re-train for bonding, and the host that has "lower" UUID just waits
for this to happen. To support this split setting the link width and
triggering the actual bonding a separate functions that can be called as
needed.

While there remove duplicated empty line in the kernel-doc comment of
tb_port_lane_bonding_disable().

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