thunderbolt: Use bit 31 to check if Firmware CM is running in Tiger Lake

In Tiger Lake the Firmware CM is always enabled (so bit 0 is always set)
but it may be in "pass through" mode which means it requires Software CM
instead. This can be determined by checking bit 31 instead.

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