Description of change

I've given a shot at the broadcast feature (#37). It's far from a perfect, but I'm hoping it gets the ball rolling, and I might use it in our next project.

What I like in this version:

• It seems to work. 🤓
• The changes don't spill over too many parts of the code, and are mostly in the BroadcastLogic class, with a few changes in the addr_decode logic.

What I don't like:

• Currently not checking properly that the broadcaster and target have the same type.
• Building the broadcast_map was rather painful, I'm sure there is a better way?
• Broadcast to arrays requires listing each element individually (limitation in the systemrdl-compiler apparently).
• When broadcasting to an array, all elements must be listed in the broadcast target (no partial selection).
• Doesn't support broadcast to memories.
• Not tested thoroughly the impact of nested regfile broadcasts, or more complex address map structures.

Checklist

• I have reviewed this project's contribution guidelines
• This change has been tested and does not break any of the existing unit tests. (if unable to run the tests, let us know)
• If this change adds new features, I have added new unit tests that cover them.