platform/x86: thinkpad_acpi: sysfs interface to auxmac

Newer Thinkpads have a feature called MAC Address Pass-through.
This patch provides a sysfs interface that userspace can use
to get this auxiliary mac address.

Signed-off-by: Fernando Eckhardt Valle <fevalle@ipt.br>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20230926202144.5906-1-fevalle@ipt.br


Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>