Docs/ABI/damon: document obsolete_target sysfs file

Update DAMON ABI document for the newly added obsolete_target DAMON sysfs
file.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: SeongJae Park <[e-mail]>
Reviewed-by: Bijan Tabatabai <[e-mail]>
Cc: David Hildenbrand <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Cc: Liam Howlett <[e-mail]>
Cc: Lorenzo Stoakes <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Mike Rapoport <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Cc: Suren Baghdasaryan <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

Documentation/ABI/testing/sysfs-kernel-mm-damon

···
 		the target process if the context is for virtual address spaces
 		monitoring, respectively.
 
+What:		/sys/kernel/mm/damon/admin/kdamonds/<K>/contexts/<C>/targets/<T>/obsolete_target
+Date:		Oct 2025
+Contact:	SeongJae Park <[e-mail]>
+Description:	Writing to and reading from this file sets and gets the
+		obsoleteness of the matching parameters commit destination
+		target.
+
 What:		/sys/kernel/mm/damon/admin/kdamonds/<K>/contexts/<C>/targets/<T>/regions/nr_regions
 Date:		Mar 2022
 Contact:	SeongJae Park <[e-mail]>