KVM: s390: Add a routine for setting userspace CPU state

KVM: s390: Add a routine for setting userspace CPU state

This capability exists, but we don't record anything when userspace
enables it. Let's refactor that code so that a note can be made in
the debug logs that it was enabled.

Signed-off-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20211008203112.1979843-7-farman@linux.ibm.com
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>