s390/uv: Update PG_arch_1 comment

We removed the usage of PG_arch_1 for page tables in commit
a51324c4 ("s390/cmma: rework no-dat handling").

Let's update the comment in UV to reflect that.

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20240508182955.358628-6-david@redhat.com


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