Make it a generic hook rather than a KVM hook.  Less code and
ifdeffery.

Since the only user of the hook is old S390 KVM, there's hope we can
get rid of it some day.
Acked-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Acked-by: NLaszlo Ersek <lersek@redhat.com>
Acked-by: NStefano Stabellini <stefano.stabellini@eu.citrix.com>
Message-id: 1375276272-15988-5-git-send-email-armbru@redhat.com
Signed-off-by: NAnthony Liguori <anthony@codemonkey.ws>