mm/damon/sysfs-schemes: implement fail_charge_{num,denom} files

mm/damon/sysfs-schemes: implement fail_charge_{num,denom} files

Implement the user-space ABI for the DAMOS action failed region
quota-charge ratio setup.  For this, add two new sysfs files under the
DAMON sysfs interface for DAMOS quotas.  Names of the files are
fail_charge_num and fail_charge_denom, and work for reading and setting
the numerator and denominator of the failed regions charge ratio.

Link: https://lore.kernel.org/20260428013402.115171-5-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>