mm/page_owner: add struct stack_print_ctx.flags

mm/page_owner: add struct stack_print_ctx.flags

Add the flags field to stack_print_ctx, and define two flags for current
behavior (printing stack traces and their number of base pages).

The plumbing of flags is debugfs_create_file(data) -> inode.i_private ->
page_owner_stack_open() -> stack_print_ctx.flags -> stack_print().

No behavior change intended.

Link: https://lkml.kernel.org/r/20251001175611.575861-3-mfo@igalia.com
Signed-off-by: Mauricio Faria de Oliveira <mfo@igalia.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>