mem-cache: Implement FPC-D cache compression

mem-cache: Implement FPC-D cache compression

Implementation of Frequent Pattern Compression with limited Dictionary
support (FPC-D) cache compressor, as described in "Opportunistic
Compression for Direct-Mapped DRAM Caches", by Alameldeen et al.

Change-Id: I26cc1646f95400b6a006f89754f6b2952f5b4aeb
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/21154
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>