mm: tidy up shmem mTHP controls and stats

Previously we had a situation where shmem mTHP controls and stats were not
exposed for some supported sizes and were exposed for some unsupported
sizes.  So let's clean that up.

Anon mTHP can support all large orders [2, PMD_ORDER].  But shmem can
support all large orders [1, MAX_PAGECACHE_ORDER].  However, per-size
shmem controls and stats were previously being exposed for all the anon
mTHP orders, meaning order-1 was not present, and for arm64 64K base
pages, orders 12 and 13 were exposed but were not supported internally.

Tidy this all up by defining ctrl and stats attribute groups for anon and
file separately.  Anon ctrl and stats groups are populated for all orders
in THP_ORDERS_ALL_ANON and file ctrl and stats groups are populated for
all orders in THP_ORDERS_ALL_FILE_DEFAULT.

Additionally, create "any" ctrl and stats attribute groups which are
populated for all orders in (THP_ORDERS_ALL_ANON |
THP_ORDERS_ALL_FILE_DEFAULT).  swpout stats use this since they apply to
anon and shmem.

The side-effect of all this is that different hugepage-*kB directories
contain different sets of controls and stats, depending on which memory
types support that size.  This approach is preferred over the alternative,
which is to populate dummy controls and stats for memory types that do not
support a given size.

[[email protected]: file pages and shmem can also be split]
  Link: https://lkml.kernel.org/r/[email protected]: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ryan Roberts <[email protected]>
Tested-by: Barry Song <[email protected]>
Reviewed-by: Baolin Wang <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Gavin Shan <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Lance Yang <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

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