mm/damon/sysfs-schemes: add a file for setting damos_filter->allow

Only kernel-space DAMON API users can use inclusive DAMOS filters.  Add a
sysfs file named 'allow' under DAMOS filter directory of DAMON sysfs
interface, to let the user-space users use inclusive DAMOS filters.

Link: https://lkml.kernel.org/r/20250109175126.57878-7-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>