gpio_intel: Support integrated GPIO controllers of the Cherry Trail SoC.

gpio_intel: Support integrated GPIO controllers of the Cherry Trail SoC.

* The gpio_acpi module takes care of probing and setting up the ACPI
  GPIO-signaled events and the ACPI address space handler, utilizing the
  gpio interface provided by gpio_intel for the actual GPIO accesses.

* So far gpio_intel can only be used for the ACPI-5.0 GPIO features.

* This makes ACPI gpio events (which replace GPE interrupts on many
  current x86 SoC devices) work, and provides a handler for the
  GeneralPurposeIo Opregions of each GPIO controller.

* With this the HP x2 210 detachable correctly recognizes unplugging
  of the power supply, and opening/closing of the lid.

* Further work is still needed to refactor gpio_intel to make adding
  support for other SoC/CPU versions easier.

* The gpio_if.m interface is still a prototype that only provides a
  minimum of functionality that is needed to get  gpio_acpi working.