pinctrl: mediatek: emulate GPIO interrupt on both-edges

MTK EINT does not support generating interrupt on both edges.
Emulate this by changing edge polarity while enable irq,
set types and interrupt handling. This follows an example of
drivers/gpio/gpio-mxc.c.

Signed-off-by: Yingjoe Chen <yingjoe.chen@mediatek.com>
Signed-off-by: Chaotian Jing <chaotian.jing@mediatek.com>
Acked-by: Hongzhou Yang <hongzhou.yang@mediatek.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>