Add an example of PEvent usage to the model

[klingaard]

The Sparta modeling framework supports PEvents or Performance Events useful for correlating the performance model against other models like RTL. The format for PEvents is somewhat hard-coded, unfortunately, but in Sparta it's built on top of the logging mechanism which can be extended to different formats.

For this issue, I'll add a few PEvents to the model:

1. One at Retire/ROB completion
2. One at Decode
3. One at Rename

CC @gvenkatagiri

[klingaard]

Work complete.