gpio / ACPI: Move event handling registration to gpiolib irqchip helpers

Since now we have irqchip helpers that the GPIO chip drivers are supposed
to use if possible, we can move the registration of ACPI events to happen
in these helpers. This seems to be more natural place and might encourage
GPIO chip driver writers to take advantage of the irqchip helpers.

We make the functions available to GPIO chip drivers via private gpiolib.h,
just in case generic irqchip helpers are not suitable.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>