UPSTREAM: arch: setup PF_IO_WORKER threads like PF_KTHREAD

[ Upstream commit 4727dc20 ]

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().

Change-Id: Iec4a3c42a39f016b323476d7238f3d36aaf0e6cf
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 320c8057)
Bug: 268174392
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>