mem-cache: Create CPack compressor

Implementation of C-Pack, as described in "C-Pack: A High-
Performance Microprocessor Cache Compression Algorithm".

C-Pack uses pattern matching schemes to detect and compress
frequently appearing data patterns. As in the original paper,
it divides the input in 32-bit words, and uses 6 patterns to
match with its dictionary.

For the patterns, each letter represents a byte: Z is a null
byte, M is a dictionary match, X is a new value. The patterns
are ZZZZ, XXXX, MMMM, MMXX, ZZZX, MMMX.

Change-Id: I2efc9db2c862620dcc1155300e39be558f9017e0
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/11105
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>