[cherry-pick][BugFix] Support setting tp=1 for the Eagle draft model to take effect

[zhaomingyu13]

According to the official documentation, the parameter "draft_tensor_parallel_size": 1 is supposed to be applied to the Eagle3 model. However, based on actual debugging, it was found that the number of tensor parallelisms (tp) of the Eagle model is consistent with that of the target model. The setting of tp for the draft model did not take effect as expected.

Note: This feature has not been superimposed and tested with sp and dp. It will be adapted later
No

from vllm import LLM, SamplingParams

def main():
    prompts = [
        "The future of AI is",
    ]
    sampling_params = SamplingParams(temperature=0.8, top_p=0.95)
    llm = LLM(
            model="meta-llama/Llama-3.1-8B-Instruct",
            tensor_parallel_size=4,
            gpu_memory_utilization=0.9,
            enforce_eager=True,
            speculative_config={
                "method": "eagle3",
                "model": "yuhuili/EAGLE3-LLaMA3.1-Instruct-8B"
                "draft_tensor_parallel_size": 1,
                "num_speculative_tokens": 3,
            },
        )
    outputs = llm.generate(prompts, sampling_params)
    print(f"Outputs: {outputs}")
    for output in outputs:
        prompt = output.prompt
        generated_text = output.outputs[0].text
        print(f"Prompt: {prompt!r}, Generated text: {generated_text!r}")

pick-from: #5519
Fixes vllm-project/vllm#31345

What this PR does / why we need it?

Does this PR introduce any user-facing change?

How was this patch tested?