mm/damon/paddr: introduce DAMOS_MIGRATE_COLD action for demotion

This patch introduces DAMOS_MIGRATE_COLD action, which is similar to
DAMOS_PAGEOUT, but migrate folios to the given 'target_nid' in the sysfs
instead of swapping them out.

The 'target_nid' sysfs knob informs the migration target node ID.

Here is one of the example usage of this 'migrate_cold' action.

  $ cd /sys/kernel/mm/damon/admin/kdamonds/<N>
  $ cat contexts/<N>/schemes/<N>/action
  migrate_cold
  $ echo 2 > contexts/<N>/schemes/<N>/target_nid
  $ echo commit > state
  $ numactl -p 0 ./hot_cold 500M 600M &
  $ numastat -c -p hot_cold

  Per-node process memory usage (in MBs)
  PID             Node 0 Node 1 Node 2 Total
  --------------  ------ ------ ------ -----
  701 (hot_cold)     501      0    601  1101

Since there are some common routines with pageout, many functions have
similar logics between pageout and migrate cold.

damon_pa_migrate_folio_list() is a minimized version of
shrink_folio_list().

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Honggyu Kim <[email protected]>
Signed-off-by: Hyeongtak Ji <[email protected]>
Signed-off-by: SeongJae Park <[email protected]>
Cc: Gregory Price <[email protected]>
Cc: Hyeonggon Yoo <[email protected]>
Cc: Masami Hiramatsu (Google) <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Rakie Kim <[email protected]>
Cc: Steven Rostedt (Google) <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

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