mips: alchemy: gpio: Include the right header

The local GPIO driver in the MIPS Alchemy is including the legacy
<linux/gpio.h> header but what it wants is to implement a GPIO
driver so include <linux/gpio/driver.h> instead.

Cc: Bartosz Golaszewski <brgl@bgdev.pl>
Cc: linux-gpio@vger.kernel.org
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>