[Bugfix] fix logging and d2h bug for flash comm1 (#3505)

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

Fix 3 bugs in flash comm1 of Allgather
EP(https://github.com/vllm-project/vllm-ascend/pull/3334):
1. call `enable_sp()` with argument `vllm_config` trigger a lot of
warning log, this PR caches its return value.
2. `num_tokens_after_padding` should be cpu tensor as it will used as
`num_tokens_across_dp_cpu` in `DPMetadata`. It will causes may d2h copy
when running model.
3. In PD, model runner will execute `kv_connector_no_forward`，where
`num_tokens` is None

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

---------

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

vllm_ascend/worker/model_runner_v1.py

@@ -815,7 +815,7 @@ class NPUModelRunner(LoRAModelRunnerMixin):
         # Create a tensor for num_tokens_after_padding
         num_tokens_after_padding = torch.tensor([max_tokens_across_dp] *
                                                 self.dp_size,
-                                                device="npu",
+                                                device="cpu",
                                                 dtype=torch.int32)
 
         return max_tokens_across_dp, num_tokens_after_padding, global_with_prefill, global_enable_dbo