mm: add private field of first tail to struct page and struct folio

Allow struct folio to store hugetlb metadata that is contained in the
private field of the first tail page.  On 32-bit, _private_1 aligns with
page[1].private.

Link: https://lkml.kernel.org/r/20220922154207.1575343-3-sidhartha.kumar@oracle.com


Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Colin Cross <ccross@google.com>
Cc: David Howells <dhowells@redhat.com>
Cc: "Eric W . Biederman" <ebiederm@xmission.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: kernel test robot <lkp@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: William Kucharski <william.kucharski@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>