KVM: s390: fix missing present bit for gmap puds

For hugetlbs, gmap puds have the present bit set. For normal puds (which
point to ptes), the bit is not set. This is in contrast to the normal
userspace puds, which always have the bit set for present pmds.

This causes issues when ___pte_offset_map() is modified to only check for
the present bit.

The solution to the problem is simply to always set the present bit for
present gmap pmds.

Link: https://lkml.kernel.org/r/20251028130150.57379-2-imbrenda@linux.ibm.com
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Link: https://lore.kernel.org/lkml/20251017144924.10034-1-borntraeger@linux.ibm.com/
Tested-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Acked-by: Balbir Singh <balbirs@nvidia.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Dave Airlie <airlied@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Francois Dugast <francois.dugast@intel.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Lyude <lyude@redhat.com>
Cc: Mathew Brost <matthew.brost@intel.com>
Cc: Mika Penttilä <mpenttil@redhat.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>