mm/damon/lru_sort: enable and disable synchronously

Writing a value to DAMON_RECLAIM's 'enabled' parameter turns on or off
DAMON in an ansychronous way.  This means the parameter cannot be used to
read the current status of DAMON_RECLAIM.  'kdamond_pid' parameter should
be used instead for the purpose.  The documentation is easy to be read as
it works in a synchronous way, so it is a little bit confusing.  It also
makes the user space tooling dirty.

There's no real reason to have the asynchronous behavior, though.  Simply
make the parameter works synchronously, rather than updating the document.

Link: https://lkml.kernel.org/r/20221025173650.90624-4-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>