selftests/damon: add tests for DAMON_LRU_SORT's enabled parameter

Add simple test cases for DAMON_LRU_SORT's 'enabled' parameter.  Those
tests are focusing on the synchronous behavior of DAMON_RECLAIM enabling
and disabling.

Link: https://lkml.kernel.org/r/20221025173650.90624-5-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>