mem-cache: Create MRU replacement policy

mem-cache: Create MRU replacement policy

Implementation of a Most Recently Used replacement policy.

Change-Id: Id52cb247ca25d4523dcc53490d113695dac6a3f1
Reviewed-on: https://gem5-review.googlesource.com/8889
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>