rocketchip: must create bundles within Module scope

1. Bundles be created after base class Module constructor runs
2. Bundles must be created before Module(...) runs

Solution: pass a bundle constructor to the cake base class

Require the constructor to take a parameter so people don't use it by
accident; they should get a type error.

Consistently name all the cake arguments with an _io, _coreplex, _outer,
so that they don't shadow the base class variables you should be using.