mm,page_ext: derive the node from the pfn

mm,page_ext: derive the node from the pfn

page_ext is the only user of 'status_change_nid', which is set in
online/offline operations, to know to which node we are adding/removing
memory.

Prior to call any notifiers, the memmap is initialized via, which among
other things, sets the node the pages belong to, to all corresponging
pages.  This means that there is no need to keep using 'status_change_nid'
since we can derive the node from the pfn.  This will allow us to finally
drop 'status_change_nid' from the memory_notify struct.

Link: https://lkml.kernel.org/r/20250616135158.450136-11-osalvador@suse.de
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Suggested-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Joanthan Cameron <Jonathan.Cameron@huawei.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>