mem-cache: Add a repeated value pattern to compressors

mem-cache: Add a repeated value pattern to compressors

The repeated value pattern checks if values are composed of multiple
instances of the same value. If successful, the bits of the repeated
value are included only once in the compressed data.

Change-Id: Ia7045b4e33a91fd8d712fe1ca689f7f8cb4e5feb
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/21153
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>