Laptop: let ATKACPI.sys (ASUS) load, register ACPIEC GPE interrupt with ACPI if requested

This patch implements AcpiInterfaceConnect(Disconnect)Vector, AcpiInterfaceNotificationsRegister(Unregister).
At least I think it's the right way. Some (all?) of this code is selected by trial and error.
With this ATKACPI.sys loads; MS ACPIEC.sys goes a bit further on boot, still failing to load. In debug log it sends unknown IOCTL to ACPI, 0x32C008.

The patch may cause 50% chance of ACPIEC.sys hanging at AddDevice when installed through Device Manager (but that doesn't happen on boot, where it always just says that AddDevice failed). Don't know why.. Don't know if its status code in Device manager always randomly alternating when started system with that installed ("device is not working properly because FIXME is not working properly" / "Device is not working properly or some of the drivers failed to load") has something to do with that chance.