KVM: s390: reuse kvm_s390_set_cpuflags()

Use it in all places where we set cpuflags.

Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20180123170531.13687-3-david@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>