[main] mlp weight prefetch in Qwen Dense Models (#2816)

### What this PR does / why we need it?
This PR prefetchs the weight of mlp layers in Qwen Dense Models to
optimize the performance in Decode phase mainly.

### Does this PR introduce _any_ user-facing change?
 No.

### How was this patch tested?
CI passed with new added/existing test.

- vLLM version: main
- vLLM main:
a1213fae5f

Signed-off-by: rjg-lyh <1318825571@qq.com>
Co-authored-by: Shuming19 <313093131@qq.com>

vllm_ascend/ops/activation.py

@@ -35,8 +35,10 @@ class AscendSiluAndMul(SiluAndMul):
 
         from vllm_ascend.utils import is_310p
 
+        torch.ops.vllm.maybe_prefetch_mlp_down_proj(x)
         if is_310p():
             out = torch_npu.npu_swiglu(x.to(torch.float32)).to(torch.float16)
         else:
             out = torch_npu.npu_swiglu(x)
+        torch.ops.vllm.maybe_wait_prefetch_done(out)
         return out