stdlib: Update TestBoard to work with Simulator

This change makes minor updates to the TestBoard so that it can work
nicely with the Simulator module.

This change also makes the cache hierarchy optional for the TestBoard.

Change-Id: If46d53779164e87b6fc06176355be6b4ae05aa99
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/64017
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Reviewed-by: Mahyar Samani <msamani@ucdavis.edu>
4 files changed