thunderbolt: Only stop control channel when entering freeze

According to the kernel power management documentation freeze phase
should only quiesce the device, no need to configure wakes or put it to
low power state. For this reason we simply stop the control channel and
in case of Software Connection Manager also mark the hotplug disabled.
This should align the driver better with the PM framework expectations.

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