mm/damon/tests/core-kunit: add test cases for multiple regions in damon_test_split_re...

mm/damon/tests/core-kunit: add test cases for multiple regions in damon_test_split_regions_of()

Extend damon_test_split_regions_of() to verify that it correctly handles
multiple regions with various 'min_sz_region'.

[sj@kernel.org: remove braces in damon_test_split_regions_of()]
Link: https://lkml.kernel.org/r/20251224153125.69194-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20251224042200.2061847-5-shu17az@gmail.com
Signed-off-by: Shu Anzai <shu17az@gmail.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>