selftests/damon: add a test for DAMOS apply intervals

Add a selftest for DAMOS apply intervals. It runs two schemes having
different apply interval agains an artificial memory access workload, and
check if the scheme with smaller apply interval was applied more
frequently.

Link: https://lkml.kernel.org/r/20240207203134.69976-6-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>