s390x/kvm: let the CPU model control CMM(A)

s390x/kvm: let the CPU model control CMM(A)

Starting with recent kernels, if the cmma attributes are available, we
actually have hardware support. Enabling CMMA then means providing the
guest VCPU with CMM, therefore enabling its CMM facility.

Let's not blindly enable CMM anymore but let's control it using CPU models.
For disabled CPU models, CMMA will continue to always get enabled.

Also enable it in the applicable default models.

Please note that CMM doesn't work with hugetlbfs, therefore we will
warn the user and keep it disabled. Migrating from/to a hugetlbfs
configuration works, as it will be disabled on both sides.

Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Message-Id: <20160905085244.99980-24-dahi@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>