arch: setup PF_IO_WORKER threads like PF_KTHREAD

stable inclusion
from stable-v5.10.162
commit 320c8057eceb18c5d836fcbe0ffb0035fcfe28ff
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6LQMS

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=320c8057eceb18c5d836fcbe0ffb0035fcfe28ff



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PF_IO_WORKER are kernel threads too, but they aren't PF_KTHREAD in the
sense that we don't assign ->set_child_tid with our own structure. Just
ensure that every arch sets up the PF_IO_WORKER threads like kthreads
in the arch implementation of copy_thread().

Signed-off-by: Jens Axboe <axboe@kernel.dk>

Conflict:
  arch/s390/kernel/process.c
  arch/x86/kernel/process.c
Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>