mem-cache: ReplacementPolicy specific replacement data

mem-cache: ReplacementPolicy specific replacement data

Replacement data is specific for each replacement policy, and thus
should be instantiated differently by each policy.

Touch() and reset() do not need to be aware of CacheBlk, as they
only update its ReplacementData.

Invalidate() makes replacement policies independent of cache blocks,
by removing the awareness of the valid state.

An inheritable base ReplaceableEntry class was created to allow usage
of replacement policies with any table-like structure.

Change-Id: I998917d800fa48504ed95abffa2f1b7bfd68522b
Reviewed-on: https://gem5-review.googlesource.com/9421
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>