[300I] support decode-only aclgraph mode (#6849)

### What this PR does / why we need it?
310p aclgraph mode, but has some problems:
- the event-id hardware limit, the num of graph will be limited.
- the cann version support this feature cannot be get from external of
huawei.
### Does this PR introduce _any_ user-facing change?
No
### How was this patch tested?
local test
- vLLM version: v0.15.0
- vLLM main:
83b47f67b1

Signed-off-by: Tflowers-0129 <2906339855@qq.com>

vllm_ascend/utils.py

@@ -833,7 +833,7 @@ def weak_ref_tensor(tensor: Any) -> Any:
     but will not keep the original tensor alive.
     """
     if isinstance(tensor, torch.Tensor):
-        return torch.ops._C_ascend.weak_ref_tensor(tensor)
+        return torch_npu._C._weak_ref_tensor(tensor)
     else:
         return tensor