s390: add kfence region to pagetable dumper

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Link: https://lore.kernel.org/r/20210728190254.3921642-5-hca@linux.ibm.com


Signed-off-by: Heiko Carstens <hca@linux.ibm.com>