mem-cache: Allow moving data contractions

mem-cache: Allow moving data contractions

Data contractions happen when a block passes from a less compressed
(e.g., uncompressed) to a more compressed (e.g., compressed) state.

Some compaction methods enforce that a block can only be allocated
in a location matches an exact compression factor, thus on data
contractions such blocks must be moved to another location, or
they must be padded to fake a bigger size.

For compaction methods that do not have that limitation, performance
can be improved if the contracted block is moved to co-allocate with
another existing entry, since it frees up an entry.

Change-Id: I302bc561b897f9d3ce1426331fe4b5c2df76f4b5
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/36578
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>