Introduce a common parent class for both cases, where kvm and non-kvm
can hook up callbacks. This will be used by follow-on patches for
adapter registration and mapping.

We now always have a flic, regardless of whether we use kvm; the
non-kvm implementation just doesn't do anything.
Reviewed-by: NJens Freimann <jfrei@linux.vnet.ibm.com>
Reviewed-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>