s390x: Implement IBK insertion in the UV Device Driver

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2111748

Patches are clean cherry-picks, except for the second one which had a simply contextual conflict (I tried to cherry-pick the required patches to solve that, too, but they caused some trouble in the CKI, so it's better to solve the conflict manually here).

Sanity checked by installing the kernel in the host and a protected guest and making sure that the guest still boots afterwards.

Signed-off-by: Thomas Huth thuth@redhat.com