pinctrl: at91: enhance (debugfs) at91_gpio_dbg_show

When a pin is configured as GPIO, print also direction (input or output).

Signed-off-by: Matthieu Crapet <mcrapet@gmail.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>