mm/madvise: split out populate behavior check logic

mm/madvise: split out populate behavior check logic

madvise_do_behavior() has a long open-coded 'behavior' check for
MADV_POPULATE_{READ,WRITE}.  It adds multiple layers[1] and make the code
arguably take longer time to read.  Like is_memory_failure(), split out
the check to a separate function.  This is not technically removing the
additional layer but discourage further extending the switch-case.  Also
it makes madvise_do_behavior() code shorter and therefore easier to read.

[1] https://lore.kernel.org/bd6d0bf1-c79e-46bd-a810-9791efb9ad73@lucifer.local

Link: https://lkml.kernel.org/r/20250312164750.59215-3-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: David Hildenbrand <david@redhat.com>
Cc: Liam R. Howlett <howlett@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>