Allow member functions to subscribe to IRQ #10
Description
There might be more than one virtio driver, in which case we'd want different instances to be notified about different IRQ's. The nicest way (I think) would be to allow the IRQ subscription system from #6 to be able to handle delegates. Another solution is polymorphism, but this gives us a little overhead (since we'll always have to look up the sub type, as long as any subclass can subscribe to any IRQ. Yet another solution: Force IRQ's into a schema (we can overwrite the defaults on the PCI device). I really don't like that solution.