mm: set pageblock_order to HPAGE_PMD_ORDER in case with !CONFIG_HUGETLB_PAGE but THP enabled

As Vlastimil suggested in previous discussion[1], it doesn't make sense to
set pageblock_order as MAX_PAGE_ORDER when hugetlbfs is not enabled and
THP is enabled.  Instead, it should be set to HPAGE_PMD_ORDER.

[1] https://lore.kernel.org/all/76457ec5-d789-449b-b8ca-dcb6ceb12445@suse.cz/
Link: https://lkml.kernel.org/r/3d57d253070035bdc0f6d6e5681ce1ed0e1934f7.1712286863.git.baolin.wang@linux.alibaba.com


Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>