gpio: mxc: Always set GPIOs used as interrupt source to INPUT mode

Always configure GPIO pins which are used as interrupt source as INPUTs.
In case the default pin configuration is OUTPUT, or the prior stage does
configure the pins as OUTPUT, then Linux will not reconfigure the pin as
INPUT and no interrupts are received.

Always configure the interrupt source GPIO pin as input to fix the above case.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Fixes: 07bd1a6c ("MXC arch: Add gpio support for the whole platform")
Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>