mm: hugetlb: allow hugepages_supported to be architecture specific

mm: hugetlb: allow hugepages_supported to be architecture specific

s390 has a constant hugepage size, by setting HPAGE_SHIFT we also change
e.g. the pageblock_order, which should be independent in respect to
hugepage support.

With this patch every architecture is free to define how to check
for hugepage support.

Signed-off-by: Dominik Dingel <[email protected]>
Acked-by: Martin Schwidefsky <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Christian Borntraeger <[email protected]>
Cc: Michael Holzheu <[email protected]>
Cc: Gerald Schaefer <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>