mm: memory_failure: move memory_failure_attr_group under MEMORY_FAILURE

The memory_failure_attr_group is only called if MEMORY_FAILURE enabled,
move it under this configuration.

Link: https://lkml.kernel.org/r/20230508114128.37081-1-wangkefeng.wang@huawei.com


Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Acked-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>