input: gpio_keys_polled: Add support for GPIO descriptors

GPIO descriptors are the preferred way over legacy GPIO numbers
nowadays. Convert the driver to use GPIO descriptors internally but
still allow passing legacy GPIO numbers from platform data to support
existing platforms.

Signed-off-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Acked-by: Grant Likely <grant.likely@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>