s390x/kvm: don't enable key wrapping if msa3 is disabled

s390x/kvm: don't enable key wrapping if msa3 is disabled

As the CPU model now controls msa3, trying to set wrapping keys without
msa3 being around/enable in the kernel will produce misleading errors.

So let's simply not configure key wrapping if msa3 is not enabled and
make compat machines with disabled CPU model work correctly.

Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Message-Id: <20160905085244.99980-25-dahi@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>