Zbkb, Zbkx, Zk* need to be able to be instantiated independently of Zb*
Created by: davidharrishmc
As far as I can tell in a brief code review, Zbkb requires Zbb to instantiate the zbb module.
Each of these extensions should be independent, and instantiate no more hardware than necessary.
It would be good to create derived configurations with each extension independently (as well as everything in Zkn without B), and then test those configurations in nightly to make sure they work on the relevant tests.
It would also be good to review the code and check that no hardware is generated unnecessarily for any of the configurations, such as all of Zbb when only Zbkb is requested.