sparc64:mm/hugetlb: Set correct huge_pte_count index for 8M hugepages

sparc64:mm/hugetlb: Set correct huge_pte_count index for 8M hugepages

Both set_huge_pte_at(...) and huge_ptep_get_and_clear(...)
call real_hugepage_size_to_pte_count_idx(hugepage_size) when adjusting
huge_pte_count. For 8MB/4MB the huge_pte_count index computed is 1(one).
This is incorrect because this index is for xl_hugepages. So the tsb
grow code in the mm fault path does not grow the tsb for 8MB/4MB
hugepages.

Signed-off-by: Bob Picco <bob.picco@oracle.com>
Signed-off-by: Vijay Kumar <vijay.ac.kumar@oracle.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Tested-by: Mike Kravetz <mike.kravetz@oracle.com>
Orabug: 24490586
(cherry picked from commit c928d6fccaa59bd4b6cffc904144fa67a4726ff6)
Signed-off-by: Allen Pais <allen.pais@oracle.com>