[Event] Cleanup handling of events

[alnyan]

Currently, events have to use immutably borrowed AcpiSystem due to how they're handled and stored inside AcpiSystem itself. As a consequence, they either have to queue the actions somewhere else (to be handled outside of acpi-system crate) or, as it is implemented now, return an EventAction to be taken by the AcpiSystem, I don't really like this idea and there might possibly be a better solution to this.