ARM: dts: Enable PMIC interrupts on ODROID

The ODROID kernel shows that the PMIC interrupt line is hooked up
to pin GPX3-2.

This is needed for the max77686-irq driver to create the PMIC IRQ
domain, which is needed by max77686-rtc.

Signed-off-by: Daniel Drake <drake@endlessm.com>
Tested-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Signed-off-by: Olof Johansson <olof@lixom.net>