KVM: s390: Limit guest size to 16TB
KVM: s390: Limit guest size to 16TB

Currently we fill up a full 5 level page table to hold the guest
mapping. Since commit "support gmap page tables with less than 5
levels" we can do better.
Having more than 4 TB might be useful for some testing scenarios,
so let's just limit ourselves to 16TB guest size.
Having more than that is totally untested as I do not have enough
swap space/memory.

We continue to allow ucontrol the full size.

Signed-off-by: Christian Borntraeger <49712f635b03c16d7f4c43df70e49ec8c565813d@de.ibm.com>
Acked-by: Cornelia Huck <94980dd689360e06f79e918bf71ea5fed7a2bc63@de.ibm.com>
Cc: Martin Schwidefsky <52616596d8f5df0d597e85ab515377f92f939c68@de.ibm.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs