thp, s390: disable thp for kvm host on s390

thp, s390: disable thp for kvm host on s390

This patch is part of the architecture backend for thp on s390.  It
disables thp for kvm hosts, because there is no kvm host hugepage support
so far.  Existing thp mappings are split by follow_page() with FOLL_SPLIT,
and future thp mappings are prevented by setting VM_NOHUGEPAGE in
mm->def_flags.

Signed-off-by: Gerald Schaefer <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Hillf Danton <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Heiko Carstens <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>