KVM: selftests: introduce P47V64 for s390x

s390x can have up to 47bits of physical guest and 64bits of virtual
address  bits. Add a new address mode to avoid errors of testcases
going beyond 47bits.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Message-Id: <20210608123954.10991-1-borntraeger@de.ibm.com>
Fixes: ef4c9f4f

 ("KVM: selftests: Fix 32-bit truncation of vm_get_max_gfn()")
Cc: stable@vger.kernel.org
Reviewed-by: David Matlack <dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>