target/s390x: AP-passthrough for PV guests

Enabling AP-passthrough(AP-pt) for PV-guest by using the new CPU
features for PV-AP-pt of KVM.

As usual QEMU first checks which CPU features are available and then
sets them if available and selected by user. An additional check is done
to verify that PV-AP can only be enabled if "regular" AP-pt is enabled
as well. Note that KVM itself does not enforce this restriction.

Reviewed-by: Michael Mueller <mimu@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>
Message-ID: <20230823142219.1046522-6-seiden@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>