[KVPOOl]Support pp (#4761)

### What this PR does / why we need it?
Support pp for kv pool

- vLLM version: v0.12.0
- vLLM main:
ad32e3e19c

---------

Signed-off-by: baxingpiaochong <771405853@qq.com>

vllm_ascend/distributed/kvpool/pool_worker.py

@@ -48,6 +48,8 @@ class KVPoolWorker:
         self.use_layerwise = use_layerwize
         self.tp_rank = get_tensor_model_parallel_rank()
         self.tp_size = get_tensor_model_parallel_world_size()
+        self.pp_size = parallel_config.pipeline_parallel_size
+        self.pp_rank = (parallel_config.rank // self.tp_size) % self.pp_size
 
         self.pcp_size = get_pcp_group().world_size
         self.pcp_rank = get_pcp_group(
@@ -87,6 +89,7 @@ class KVPoolWorker:
             self.head_or_tp_rank,
             self.pcp_rank,
             self.dcp_rank,
+            self.pp_rank,
         )
 
         self.token_database = ChunkedTokenDatabase(self.metadata,
@@ -555,6 +558,12 @@ class KVPoolWorker:
                         "@head_or_tp_rank:0", f"@head_or_tp_rank:{i}", 1)
                     multi_tp_keys.append(new_str)
 
+            for i in range(1, self.pp_size):
+                for item in keys:
+                    new_str = item.replace(  # type: ignore[attr-defined]
+                        "@pp_rank:0", f"@pp_rank:{i}", 1)
+                    multi_tp_keys.append(new_str)
+
             res = self.m_store.exists(
                 multi_tp_keys)  # type: ignore[assignment]
             num_block = len(keys)