mem: Handle CMO responses in the snoop filter

mem: Handle CMO responses in the snoop filter

Previously responses would either transfer the ownership of the line
or the actual data to the cache that send out the original request.
Cache clean operations are different since they bring neither data nor
ownership. When they are also invalidating the cache that send out the
original request will invalidate any existing copies. This patch
makes the snoop filter handle the cache clean responses accordingly.

Change-Id: I27165cb45b9dc57882526329c62db35f100d23df
Reviewed-by: Stephan Diestelhorst <stephan.diestelhorst@arm.com>
Reviewed-by: Sudhanshu Jha <sudhanshu.jha@arm.com>
Reviewed-by: Anouk Van Laer <anouk.vanlaer@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/5053
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>