mm/damon/sysfs-schemes: implement files for scheme quota goals setup

Implement DAMON sysfs directories and files for the goals of DAMOS quota. 
Those allow users set multiple goals for their aim, with target values. 
Users can further enter the current score value for each goal as feedback
for DAMOS.

Note that this commit is implementing only the basic file operations, and
not connecting the files with the DAMOS core logic.  Hence writing
something to the files makes no real effect.  The following commit will
connect the file operations and the core logic.

Link: https://lkml.kernel.org/r/20231130023652.50284-3-sj@kernel.org


Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendanhiggins@google.com>
Cc: David Gow <davidgow@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>