gpio: dln2: Include proper header

This driver has no business including <linux/gpio.h>, it is a
driver so include <linux/gpio/driver.h>.

GPIOF_DIR_IN/GPIOF_DIR_OUT are for consumers and should not be
used in drivers to use just 1/0 instead.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>