selftests/damon: implement test for min/max_nr_regions

Implement a kselftest for DAMON's {min,max}_nr_regions' parameters.  The
test ensures both the minimum and the maximum number of regions limit is
respected even if the workload's real number of regions is less than the
minimum or larger than the maximum limits.

Link: https://lkml.kernel.org/r/20240625180538.73134-7-sj@kernel.org


Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>