mm/damon/tests/core-kunit: avoid damos_test_commit stack warning

mm/damon/tests/core-kunit: avoid damos_test_commit stack warning

The newly added damos_test_commit() constructs multiple large structures
on the stack, which exceeds the warning limit in some cases:

In file included from mm/damon/core.c:2941:
mm/damon/tests/core-kunit.h: In function 'damos_test_commit':
mm/damon/tests/core-kunit.h:965:1: error: the frame size of 1520 bytes is larger than 1280 bytes [-Werror=frame-larger-than=]

Split this function up into two separate ones that are called
sequentially, so they can occupy the same stack slots.

Link: https://lkml.kernel.org/r/20251204100403.1034980-1-arnd@kernel.org
Fixes: 299a88f6ec13 ("mm/damon/tests/core-kunit: add damos_commit() test")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: Quanmin Yan <yanquanmin1@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>