This is a GPIO driver so include only <linux/gpio/driver.h>.
Drop the use of GPIOF_* flags: these are for consumers, not
drivers. Just return 0/1.

Cc: Stefan Agner <stefan@agner.ch>
Cc: Thierry Reding <treding@nvidia.com>
Reviewed-by: NDmitry Osipenko <digetx@gmail.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>