[Bugfix] rename enable_flash_comm_v1 back to enable_sp (#6883)

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

PR #5632 introduced a bug by replacing some branches gated by enable_sp
with enable_flash_comm_v1. As a result, when enable_shared_expert_dp is
enabled alone (i.e., VLLM_ASCEND_ENABLE_FLASHCOMM1=0 and
VLLM_ASCEND_ENABLE_FLASHCOMM=0), the behavior becomes inconsistent with
the previous logic and leads to accuracy issues. This PR restores the
original enable_sp-based branching to recover expected behavior and
accuracy.

### Does this PR introduce _any_ user-facing change?

No

### How was this patch tested?

#### 1. start server
``` bash
vllm serve /home/weights/DeepSeek-V2-Lite-W8A8/  \
    --port 8001 \
    --served-model-name auto \
    --max-model-len 1024 \
    --enforce-eager \
    --tensor-parallel-size 2 \
    --data-parallel-size 2 \
    --gpu-memory-utilization 0.9 \
    --enable-expert-parallel \
    --additional-config '{"enable_shared_expert_dp": true}'
```

#### 2. curl
```bash
curl -s http://localhost:8001/v1/chat/completions \
-H "Content-Type: application/json" \
-d '{
  "model": "auto",
  "messages": [
    {"role": "user", "content": "Hello. I have a question. Who are you?"}
  ],
  "max_tokens": 10,
  "temperature": 0.0,
  "ignore_eos_token": true
}'
```

- vLLM version: v0.16.0
- vLLM main:
15d76f74e2

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

vllm_ascend/ops/linear_op.py

@@ -70,7 +70,7 @@ from vllm_ascend.ops.flashcomm2_oshard_manager import flashcomm2_oshard_manager
 from vllm_ascend.utils import (
     enable_dsa_cp,
     enable_dsa_cp_with_layer_shard,
-    enable_flash_comm_v1,
+    enable_sp,
     flashcomm2_enable,
     get_flashcomm2_reorgnized_batch_ids,
     get_weight_prefetch_method,
@@ -466,7 +466,7 @@ class Flashcomm2OshardQKVParallelOp(CustomColumnParallelOp):
         # Matrix multiply.
         assert self.quant_method is not None
 
-        if enable_flash_comm_v1():
+        if enable_sp():
             input_ = torch.ops.vllm.maybe_all_gather_and_maybe_unpad(input_, True)
 
         # Trigger async broadcast before matmul to overlap communication.
@@ -649,7 +649,7 @@ def _get_column_parallel_op(
     if flashcomm2_oshard_manager.flashcomm2_oshard_enable():
         if any(p in prefix for p in ("qkv_proj", "conv1d", "query_key_value")):
             return Flashcomm2OshardQKVParallelOp(layer)
-    if enable_flash_comm_v1():
+    if enable_sp():
         if "shared_expert" in prefix:
             return None
         sp_column_prefix = [
@@ -688,7 +688,7 @@ def _get_row_parallel_op(
     if flashcomm2_enable():
         if "o_proj" in prefix or "out_proj" in prefix:
             return Flashcomm2OProjRowParallelOp(layer)
-    if enable_flash_comm_v1():
+    if enable_sp():
         if "shared_expert" in prefix:
             return None
         sp_row_prefixes = [