KVM: s390: Add "devname:kvm" alias.

Providing a "devname:kvm" module alias enables automatic loading of
the kvm module when /dev/kvm is opened.

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>