lib/Kconfig.debug: Default STRICT_DEVMEM to "y" on s390

lib/Kconfig.debug: Default STRICT_DEVMEM to "y" on s390

virtio-mem currently depends on !DEVMEM | STRICT_DEVMEM. Let's default
STRICT_DEVMEM to "y" just like we do for arm64 and x86.

There could be ways in the future to filter access to virtio-mem device
memory even without STRICT_DEVMEM, but for now let's just keep it
simple.

Tested-by: Mario Casquero <mcasquer@redhat.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Tested-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Link: https://lore.kernel.org/r/20241025141453.1210600-6-david@redhat.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>