Change the instruction coverage to be per-instance

[jerralph]

Create an instruction coverage component and have instances of all the different coverage desired. The lifecycle of this would be for the entire sim and different than the lifecycle of the instructions that fly by. We may want to decouple the coverage out of the decode instruction model, or keep it there but only sample in the coverage component.

One benefit here is that coverage of multiple cores can be done in the same simulation.