Add support for CPUIFs to have parameters

[hughjackson]

Expose a method to allow custom CPUIFs (and any new internal ones) to use parameters (for example to size sideband signals that do not directly get consumed by the regblock logic but pass from request to response). This has been tested with a custom interface but may need additional unit testing adding

[amykyta3]

Thanks!
I can see how this is useful.

I'm going to hold off on merging this at the moment since I may end up restructuring this slightly. I'm not too keen on having the parameter_declaration property be a naive singular string - I think it should be more structured to allow better scalability if I find other reasons to insert parameters elsewhere.

Will keep it as a reference for now.

[amykyta3]

Implemented an alternate but very similar solution which will be in the upcoming release.

Rather than providing the full string, the cpuif base class provides a list of strings, one for each parameter. For example:

    @property
    def parameters(self):
        return [
            "parameter FOO = 1",
            "parameter BAR = 2",
        ]

Thanks for the idea!