thunderbolt: Do not touch the hardware if the NHI is gone on resume

On PCs the NHI host controller is only present when there is a device
connected. When the last device is disconnected the host controller will
dissappear shortly (within 10s). Now if that happens when we are
suspended we should not try to touch the hardware anymore, so add a flag
for this and check it before we re-enable rings.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Yehezkel Bernat <yehezkel.bernat@intel.com>
Reviewed-by: Michael Jamet <michael.jamet@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Andreas Noever <andreas.noever@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>