commit 86a5bba5c252e90d264c7460e29a0b9e633777e7 upstream.

For policies which can do enough initialization from ->cpd_alloc_fn(),
make ->cpd_init_fn() optional.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Signed-off-by: NJiufei Xue <jiufei.xue@linux.alibaba.com>
Reviewed-by: NJoseph Qi <joseph.qi@linux.alibaba.com>