KVM: selftests: enable pgste option for the linker on s390

To avoid testcase failures we need to enable the pgstes. This can be
done with /proc/sys/vm/allocate_pgste or with a linker option that
creates an  S390_PGSTE program header.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
[Fixed as outlined by  kernel test robot <rong.a.chen@intel.com>]