arch: ensure parisc/powerpc handle PF_IO_WORKER in copy_thread()

In the arch addition of PF_IO_WORKER, I missed parisc and powerpc for
some reason. Fix that up, ensuring they handle PF_IO_WORKER like they do
PF_KTHREAD in copy_thread().

Reported-by: Bruno Goncalves <bgoncalv@redhat.com>
Fixes: 4727dc20

 ("arch: setup PF_IO_WORKER threads like PF_KTHREAD")
Signed-off-by: Jens Axboe <axboe@kernel.dk>