mm/damon/sysfs-schemes: implement filter directory

mm/damon/sysfs-schemes: implement filter directory

Implement DAMOS filter directory which will be located under the filters
directory.  The directory provides three files, namely type, matching, and
memcg_path.  'type' and 'matching' will be directly connected to the
fields of 'struct damos_filter' having same name.  'memcg_path' will
receive the path of the memory cgroup of the interest and later converted
to memcg id when it's committed.

Link: https://lkml.kernel.org/r/20221205230830.144349-7-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>