pagemap: rework hugetlb and thp report

pagemap: rework hugetlb and thp report

This patch moves pmd dissection out of reporting loop: huge pages are
reported as bunch of normal pages with contiguous PFNs.

Add missing "FILE" bit in hugetlb vmas.

Signed-off-by: Konstantin Khlebnikov <[email protected]>
Reviewed-by: Naoya Horiguchi <[email protected]>
Reviewed-by: Mark Williamson <[email protected]>
Tested-by:  Mark Williamson <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>