support cp&dcp (#3260)

### What this PR does / why we need it?
This PR adds the Prefill Context Parallelism (PCP) feature, which
corresponds to DCP. For specific implementation details, please refer to
the RFC https://github.com/vllm-project/vllm/issues/25749.
TL;DR: PCP enhances long-sequence inference capabilities by partitioning
the sequence dimension during the prefill stage.
### Does this PR introduce _any_ user-facing change?
The current implementation primarily includes the following changes:

Modified ModelRunner.py for CP partitioning logic for tokens;
Modified attention_v1.py and mla_v1.py to adapt the GQA/MLA backend to
PCP.
Modified block_tables.py to extend the KV cache storage based on
DCP&PCP;
Added necessary command-line arguments to control parallelism for PCP;
### How was this patch tested?


- vLLM version: v0.11.0rc3
- vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.0

---------

Signed-off-by: LookAround <lixushi@huawei.com>
Signed-off-by: chenjie <chenjie137@huawei.com>
Signed-off-by: Delphine-Nic <tanwenqin@huawei.com>
Signed-off-by: zhangsicheng5 <zhangsicheng5@huawei.com>
Signed-off-by: Feng Liu <liufeng248@huawei.com>
Signed-off-by: gaojc <1055866782@qq.com>
Signed-off-by: weiguihua2 <weiguihua2@huawei.com>
Signed-off-by: z50049692 <zhangmingwei11@huawei.com>
Co-authored-by: chenjie <chenjie137@huawei.com>
Co-authored-by: Delphine-Nic <tanwenqin@huawei.com>
Co-authored-by: zhangsicheng5 <zhangsicheng5@huawei.com>
Co-authored-by: Feng Liu <liufeng248@huawei.com>
Co-authored-by: gaojc <1055866782@qq.com>
Co-authored-by: weiguihua2 <weiguihua2@huawei.com>
Co-authored-by: z50049692 <zhangmingwei11@huawei.com>
Co-authored-by: w00896881 <wangzixuan40@huawei.com>

vllm_ascend/utils.py

@@ -648,6 +648,10 @@ def shared_expert_dp_enabled() -> bool:
     return get_ascend_config().enable_shared_expert_dp or enable_sp()
 
 
+def prefill_context_parallel_enable() -> bool:
+    return envs_ascend.VLLM_ASCEND_ENABLE_CONTEXT_PARALLEL
+
+
 def is_moe_model(vllm_config: VllmConfig):
     global _IS_MOE_MODEL
     if _IS_MOE_MODEL is None: