cpu: Fix checker cpu instantiation

cpu: Fix checker cpu instantiation

This change uses the params as instantiated from the default
constructor to create the checker cpu. If any of these parameters are
invalid for the checker cpu, the simulation will exit with a warning.

Change-Id: I0e58ed096c9ea5f413f2e9b64d8d184d9b0fc84e
Signed-off-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/21079
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>