Mediatek 65xx/81xx GIC interrupt polarity extension

Mediatek SOCs contain controllable inverter for each GIC SPI interrupt,
these can be used as GIC interrupt polarity extension.

Required properties:
- compatible: Compatible property value should be "mediatek,mt6577-intpol"

- reg: Physical base address of the int pol registers and length of memory
  mapped region.

Example:
       intpol: intpol@10200100 {
               compatible = "mediatek,mt6577-intpol";
               reg = <0x10200100 0x1c>;
       };