samples/damon: implement a DAMON module for memory tiering

samples/damon: implement a DAMON module for memory tiering

Implement a sample DAMON module that shows how self-tuned DAMON-based
memory tiering can be written.  It is a sample since the purpose is to
give an idea about how it can be implemented and perform, rather than be
used on general production setups.  Especially, it supports only two tiers
memory setup having only one CPU-attached NUMA node.

[sj@kernel.org: fix wrong DAMON attrs setting]
Link: https://lkml.kernel.org/r/20250510220932.47722-1-sj@kernel.org
[sj@kernel.org: trigger build even if only mtier is enabled]
Link: https://lkml.kernel.org/r/20250426184054.11437-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20250420194030.75838-8-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Yunjeong Mun <yunjeong.mun@sk.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>