mem-cache: Fix promoting of targets that need writable

mem-cache: Fix promoting of targets that need writable

There are cases where a request which does not need a writable copy
gets an response upgraded reponse and fills in a writable copy. When
this happens, we promote deferred MSHR targets that were deferred
because they needed a writable copy to service them immediately.

Previously, we would uncoditionally promote deferred targets. Since
the deferred targets might contain a cache invalidation operation, we
have to make sure that any targets following the cache invalidation is
not promoted.

Change-Id: I1f7b28f7d35f84329e065c8f63117db21852365a
Reviewed-on: https://gem5-review.googlesource.com/11016
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>