mm/damon/sysfs: support DAMON-based Operation Schemes

This commit makes DAMON sysfs interface supports the DAMON-based operation
schemes (DAMOS) feature.  Specifically, this commit adds 'schemes'
directory under each context direcotry, and makes kdamond 'state' file
writing respects the contents in the directory.

Note that this commit doesn't support all features of DAMOS but only the
target access pattern and action feature.  Supports for quotas,
prioritization, watermarks will follow.

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    <- NEW DIRECTORY
    │ │ │ │ │ │ 0/action
    │ │ │ │ │ │ │ access_pattern/
    │ │ │ │ │ │ │ │ sz/min,max
    │ │ │ │ │ │ │ │ nr_accesses/min,max
    │ │ │ │ │ │ │ │ age/min,max
    │ │ │ │ │ │ ...
    │ │ │ │ ...
    │ │ ...

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: SeongJae Park <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Xin Hao <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: sjp38