s390x: Add unpack facility feature to GA1

s390x: Add unpack facility feature to GA1

The unpack facility is an indication that diagnose 308 subcodes 8-10
are available to the guest. That means, that the guest can put itself
into protected mode.

Once it is in protected mode, the hardware stops any attempt of VM
introspection by the hypervisor.

Some features are currently not supported in protected mode:
     * vfio devices
     * Migration
     * Huge page backings

Signed-off-by: Christian Borntraeger <[email protected]>
Signed-off-by: Janosch Frank <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Reviewed-by: Claudio Imbrenda <[email protected]>
Reviewed-by: Cornelia Huck <[email protected]>
Message-Id: <20200319131921[email protected]>
Signed-off-by: Cornelia Huck <[email protected]>