thunderbolt: Add support for retimer NVM upgrade when there is no link

With help from platform firmware (ACPI) it is possible to power on
retimers even when there is no USB4 link (e.g nothing is connected to
the USB4 ports). This allows us to bring the USB4 sideband up so that we
can access retimers and upgrade their NVM firmware.

If the platform has support for this, we expose two additional
attributes under USB4 ports: offline and rescan. These can be used to
bring the port offline, rescan for the retimers and put the port online
again. The retimer NVM upgrade itself works the same way than with cable
connected.

Signed-off-by: Rajmohan Mani <rajmohan.mani@intel.com>
Co-developed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>