tests: Adding tests for gem5stats.

This change adds the first of many tests for the gem5stats.
The current test only considers a setup consisiting of
traffic generator, cache and memory.

Change-Id: I3ebe16131aed5bf6dad68de673f9491f1bea1c78
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/55743
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
3 files changed