mm/damon/core: support multiple metrics for quota goal

DAMOS quota auto-tuning asks users to assess the current tuned quota and
provide the feedback in a manual and repeated way.  It allows users
generate the feedback from a source that the kernel cannot access, and
writing a script or a function for doing the manual and repeated feeding
is not a big deal.  However, additional works are additional works, and it
could be more efficient if DAMOS could do the fetch itself, especially in
case of DAMON sysfs interface use case, since it can avoid the context
switches between the user-space and the kernel-space, though the overhead
would be only trivial in most cases.  Also in many cases, feedbacks could
be made from kernel-accessible sources, such as PSI, CPU usage, etc.  Make
the quota goal to support multiple types of metrics including such ones.

Link: https://lkml.kernel.org/r/20240219194431.159606-13-sj@kernel.org


Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>