gpio: intel-mid: switch to using gpiolib irqchip helpers

This switches the Intel MID GPIO driver over to using the gpiolib
irqchip helpers in the gpiolib core.

Cc: xinhui.pan <xinhuiX.pan@intel.com>
Acked-by: David Cohen <david.a.cohen@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>