mem: Use using to expose a print method that would otherwise be hidden.

mem: Use using to expose a print method that would otherwise be hidden.

This method would be hidden in the subclass which upset clang 11, and
that caused the build to break.

Change-Id: Ie678fc96a26809eb8f2acd0bddc1df81c0a9aa1e
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/25227
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>