hugetlbfs: New huge_add_to_page_cache helper routine

hugetlbfs: New huge_add_to_page_cache helper routine

Currently, there is only a single place where hugetlbfs pages are added
to the page cache.  The new fallocate code be adding a second one, so
break the functionality out into its own helper.

Signed-off-by: Dave Hansen <[email protected]>
Signed-off-by: Mike Kravetz <[email protected]>
Reviewed-by: Naoya Horiguchi <[email protected]>
Acked-by: Hillf Danton <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Aneesh Kumar <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Michal Hocko <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>