[V1] Make V1 engine backward compatible (#637)

### What this PR does / why we need it?
Enforce eager mode in the V1 engine ahead of the upcoming CANN and
torch_npu releases.

### Does this PR introduce _any_ user-facing change?
After this change, users will no longer need to manually set
enforce_eager=True.

### How was this patch tested?
Test it with regular offline inference examples.

Signed-off-by: Yizhou Liu <liu_yizhou@outlook.com>

tests/multicard/test_offline_inference_distributed.py

@@ -47,7 +47,6 @@ def test_models_distributed(model: str,
             dtype=dtype,
             tensor_parallel_size=4,
             distributed_executor_backend=distributed_executor_backend,
-            enforce_eager=True,
     ) as vllm_model:
         vllm_model.generate_greedy(example_prompts, max_tokens)