toshiba-acpi: Port to new backlight interface selection API

Port the backlight selection logic to the new backlight interface
selection API.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Azael Avalos <coproscefalo@gmail.com>
Acked-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>