vulkan,anv: Add a trivial implementation of VK_KHR_deferred_host_operation

This isn't actually capable of deferring anything; it just trivially returns success. The important thing here is that it's being built as shared infrastructure so, hopefully, ANV and RADV can share a tasking system. I've not implemented the guts of this yet because RT pipeline compilation in ANV is still a but of a mess thanks to the juggling we have to do around descriptor sets right now. I don't want to try to defer it until it's a bit closer to final form.