lib/stackdepot: move stack_record struct definition into the header

lib/stackdepot: move stack_record struct definition into the header

[ Upstream commit 8151c7a35d8bd8a12e93538ef7963ea209b6ab41 ]

In order to move the heavy lifting into page_owner code, this one needs to
have access to the stack_record structure, which right now sits in
lib/stackdepot.c.  Move it to the stackdepot.h header so page_owner can
access stack_record's struct fields.

Link: https://lkml.kernel.org/r/20240215215907.20121-3-osalvador@suse.de
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Marco Elver <elver@google.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Stable-dep-of: a6c1d9cb9a68 ("stackdepot: rename pool_index to pool_index_plus_1")
Signed-off-by: Sasha Levin <sashal@kernel.org>