pinctrl: mediatek: add input-enable setting in gpio_request_enable

Since input-disable cuts off input signal of gpio, add input-enable
setting in .gpio_request_enable implementation to ensure gpio function well

Signed-off-by: Biao Huang <biao.huang@mediatek.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>