mm/damon/sysfs: support DAMOS watermarks

mm/damon/sysfs: support DAMOS watermarks

This commit makes DAMON sysfs interface supports the DAMOS watermarks
feature.  Specifically, this commit adds 'watermarks' directory under each
scheme directory and makes kdamond 'state' file writing respects the
contents in the directory.

As a result, the files hierarchy becomes as below:

    /sys/kernel/mm/damon/admin
    │ kdamonds/nr_kdamonds
    │ │ 0/state,pid
    │ │ │ contexts/nr_contexts
    │ │ │ │ 0/operations
    │ │ │ │ │ monitoring_attrs/intervals/sample_us,aggr_us,update_us
    │ │ │ │ │ │ nr_regions/min,max
    │ │ │ │ │ targets/nr_targets
    │ │ │ │ │ │ 0/pid_target
    │ │ │ │ │ │ │ regions/nr_regions
    │ │ │ │ │ │ │ │ 0/start,end
    │ │ │ │ │ │ │ │ ...
    │ │ │ │ │ │ ...
    │ │ │ │ │ schemes/nr_schemes
    │ │ │ │ │ │ 0/action
    │ │ │ │ │ │ │ access_pattern/
    │ │ │ │ │ │ │ │ sz/min,max
    │ │ │ │ │ │ │ │ nr_accesses/min,max
    │ │ │ │ │ │ │ │ age/min,max
    │ │ │ │ │ │ │ quotas/ms,sz,reset_interval_ms
    │ │ │ │ │ │ │ │ weights/sz_permil,nr_accesses_permil,age_permil
    │ │ │ │ │ │ │ watermarks/    <- NEW DIRECTORY
    │ │ │ │ │ │ │ │ metric,interval_us,high,mid,lo
    │ │ │ │ │ │ ...
    │ │ │ │ ...
    │ │ ...

Link: https://lkml.kernel.org/r/20220228081314.5770-10-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Xin Hao <xhao@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>