mm, madvise: move madvise_set_anon_name() down the file

mm, madvise: move madvise_set_anon_name() down the file

Preparatory change so that we can use madvise_lock()/unlock() in the
function without forward declarations or more thorough shuffling.

No functional change.  Move as a separate commit helps git heuristics to
detect it properly.

Link: https://lkml.kernel.org/r/20250624-anon_name_cleanup-v2-3-600075462a11@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Colin Cross <ccross@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>