[Feat][SP] Suport SP for VL MoE models (#7044)

### What this PR does / why we need it?

2nd PR for https://github.com/vllm-project/vllm-ascend/issues/5712,
extend SP to VL MoE models.


### Does this PR introduce _any_ user-facing change?
remove `sp_threshold` in additional config and reuse `sp_min_token_num`
from vLLM.


### How was this patch tested?
- Model: Qwen3-VL-30B-A3B, 
- TP4 DP2
- 100 reqs
- max concurrency 1

| Seq length | Mean TTFT (ms) main | Mean TTFT (ms) this PR |
|------------|---------------------|------------------------|
| 4k         | 429.40               | 323.3                  |
| 16k        | 1297.01              | 911.74                |

- vLLM version: v0.16.0
- vLLM main:
4034c3d32e

---------

Signed-off-by: realliujiaxu <realliujiaxu@163.com>

docs/source/user_guide/configuration/additional_config.md

@@ -44,7 +44,6 @@ The following table lists additional configuration options available in vLLM Asc
 | `pa_shape_list`                     | list | `[]`    | The custom shape list of page attention ops.                                                              |
 | `enable_kv_nz`                      | bool | `False` | Whether to enable KV cache NZ layout. This option only takes effects on models using MLA (e.g., DeepSeek).                                      |
 | `layer_sharding` | dict | `{}` | Configuration options for Layer Sharding Linear |
-| `sp_threshold` | int | `1000` | For dense models, only num_tokens > threshold will enable sequence parallelism. |
 
 The details of each configuration option are as follows: