### What this PR does / why we need it?
Enable `ACL_OP_INIT_MODE=1` directly only when using V0 spec decode.
Find more details at **mengwei805**'s comment in
https://github.com/vllm-project/vllm-ascend/pull/1123.
### Does this PR introduce _any_ user-facing change?
The user will not be aware of `VLLM_ASCEND_ACL_OP_INIT_MODE`
(`ACL_OP_INIT_MODE`).
### How was this patch tested?
Test scripts:
```python
from vllm import LLM, SamplingParams
prompts = [
"The future of AI is",
]
sampling_params = SamplingParams(temperature=0.8, top_p=0.95)
llm = LLM(
model="Qwen/Qwen2.5-1.5B-Instruct",
tensor_parallel_size=1,
speculative_config={
"method": "ngram",
"num_speculative_tokens": 5,
"prompt_lookup_max": 4,
},
)
outputs = llm.generate(prompts, sampling_params)
for output in outputs:
prompt = output.prompt
generated_text = output.outputs[0].text
print(f"Prompt: {prompt!r}, Generated text: {generated_text!r}")
```
Results:
```
Adding requests: 100%|██████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 1/1 [00:00<00:00, 76.70it/s]
Processed prompts: 100%|███████████████████████████████████████████████████████████████| 1/1 [00:00<00:00, 1.33it/s, est. speed input: 6.64 toks/s, output: 21.26 toks/s]
Prompt: 'The future of AI is', Generated text: ' bright\n\n04/15/2020\n\nBy: James'
```
---------
Signed-off-by: shen-shanshan <467638484@qq.com>
2cd8ecdc4f