Add data/instruction prefetcher

[klingaard]

Similar to requirements of a branch prediction API, add a prefetching API to Olympia and integrate or implement basic data/instruction prefetchers into the model.

The effort would be:

• Design and propose a prefetching API
• Add testing for that API
• Integrate into existing Ldst/Fetch blocks and test

[Shubhf]

Hey @rajatbhatia1 @klingaard Can I take up this issue?