MacBooks provides custom ACPI methods to toggle the GPIOs for device
wake and shutdown instead of accessing the pins directly.  Prepare for
their support by adding callbacks to toggle the GPIOs, which on non-Macs
do nothing more but call gpiod_set_value().

No functional change intended.
Suggested-and-reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>