io_uring: extend task put optimisations

Now with IRQ completions done via IRQ, almost all requests freeing
are done from the context of submitter task, so it makes sense to
extend task_put optimisation from io_req_free_batch_finish() to cover
all the cases including task_work by moving it into io_put_task().

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/824a7cbd745ddeee4a0f3ff85c558a24fd005872.1629302453.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>