mm/madvise: split out madvise() behavior execution

Split out the madvise behavior applying logic from do_madvise() to make
it easier to reuse from the following change.

Link: https://lkml.kernel.org/r/20250206061517.2958-4-sj@kernel.org


Signed-off-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <howlett@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>