selftests/damon/_damon_sysfs: support DAMOS target_nid setup

_damon_sysfs.py contains code for test-purpose DAMON sysfs interface
control. Add support of DAMOS action destination target_nid setup for
more tests.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: SeongJae Park <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

tools/testing/selftests/damon/_damon_sysfs.py

···
     ops_filters = None
     filters = None
     apply_interval_us = None
+    target_nid = None
     dests = None
     idx = None
     context = None
···
 
     def __init__(self, action='stat', access_pattern=DamosAccessPattern(),
                  quota=DamosQuota(), watermarks=DamosWatermarks(),
-                 core_filters=[], ops_filters=[], filters=[],
+                 core_filters=[], ops_filters=[], filters=[], target_nid=0,
                  dests=DamosDests(), apply_interval_us=0):
         self.action = action
         self.access_pattern = access_pattern
···
         self.filters = DamosFilters(name='filters', filters=filters)
         self.filters.scheme = self
 
+        self.target_nid = target_nid
         self.dests = dests
         self.dests.scheme = self
 
···
         if err is not None:
             return err
         err = self.filters.stage()
+        if err is not None:
+            return err
+
+        err = write_file(os.path.join(self.sysfs_dir(), 'target_nid'), '%d' %
+                         self.target_nid)
         if err is not None:
             return err