mem-cache: Create BDI Compressor

Implement Base-Delta-Immediate compression, as described in
'Base-Delta-Immediate Compression: Practical Data Compression
for On-Chip Caches'

Change-Id: I7980c340ab53a086b748f4b2108de4adc775fac8
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/11412
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>