mm: move hugetlb specific things in folio to page[3]

Let's just move the hugetlb specific stuff to a separate page, and stop
letting it overlay other fields for now.

This frees up some space in page[2], which we will use on 32bit to free up
some space in page[1].  While we could move these things to page[3]
instead, it's cleaner to just move the hugetlb specific things out of the
way and pack the core-folio stuff as tight as possible.  ...  and we can
minimize the work required in dump_folio.

We can now avoid re-initializing &folio->_deferred_list in hugetlb code.

Hopefully dynamically allocating "strut folio" in the future will further
clean this up.

Link: https://lkml.kernel.org/r/20250303163014.1128035-5-david@redhat.com


Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Andy Lutomirks^H^Hski <luto@kernel.org>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcow (Oracle) <willy@infradead.org>
Cc: Michal Koutn <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: tejun heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zefan Li <lizefan.x@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>