mm/damon/sysfs-schemes: implement core_filters and ops_filters directories

Implement two DAMOS sysfs directories for managing core and operations
layer handled filters separately.  Those are named as 'core_filters' and
'ops_filters', and have files hierarchy same to 'filters'.  This commit is
only populating and cleaning up the directories, not really connecting the
files with DAMON.  Following changes will make the connections.

Link: https://lkml.kernel.org/r/20250305222733.59089-3-sj@kernel.org


Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>