samples: add a skeleton of a sample DAMON module for working set size estimation

samples: add a skeleton of a sample DAMON module for working set size estimation

Patch series "mm/damon: add sample modules".

Implement a proactive cold memory regions reclaiming logic of prcl sample
module using DAMOS.  The logic treats memory regions that not accessed at
all for five or more seconds as cold, and reclaim those as soon as found.

This patch (of 5):

Add a skeleton for a sample DAMON static module that can be used for
estimating working set size of a given process.  Note that it is a static
module since DAMON is not exporting symbols to loadable modules for now.
It exposes two module parameters, namely 'pid' and 'enable'.  'pid' will
specify the process that the module will estimate the working set size of.
'enable' will receive whether to start or stop the estimation.  Because
this is just a skeleton, the parameters do nothing, though.  The
functionalities will be implemented by following commits.

Link: https://lkml.kernel.org/r/20241210215030.85675-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20241210215030.85675-2-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>