### What this PR does / why we need it?
Follow up the PR https://github.com/vllm-project/vllm/pull/32618, this
PR provides async scheduling support for PP in vllm-ascend.
---
- vLLM version: v0.16.0
- vLLM main:
4034c3d32e
Signed-off-by: QiuChunshuo <qiuchunshuo@huawei.com>