[perf]Support MOE Multi-stream in Deepseek (#947)

### What this PR does / why we need it?
Support MOE inner Multi-stream for Deepseek. 
This feature requires graph mode with mc2 enabled.

---------

Signed-off-by: David9857 <985700846@qq.com>

vllm_ascend/models/deepseek_v2.py

@@ -216,6 +216,8 @@ class CustomDeepseekV2MoE(nn.Module):
 
         ascend_config = get_ascend_config()
         self.torchair_graph_enabled = ascend_config.torchair_graph_config.enabled
+        self.enable_multistream_shared_expert = \
+            ascend_config.torchair_graph_config.enable_multistream_shared_expert
 
     def forward(
             self,
@@ -238,6 +240,8 @@ class CustomDeepseekV2MoE(nn.Module):
 
         num_tokens, hidden_size = hidden_states.shape
 
+        multistream = self.enable_multistream_shared_expert and not is_prefill
+
         old_hidden_states = hidden_states.clone()
 
         if self.tp_size > 1:
@@ -259,13 +263,25 @@ class CustomDeepseekV2MoE(nn.Module):
         # router_logits: (num_tokens, n_experts)
         router_logits, _ = self.gate(hidden_states)
 
+        kwargs = {}
+        if multistream:
+            kwargs.update({
+                "shared_experts": self.shared_experts,
+                "shared_hidden_states": old_hidden_states
+            })
+
         hidden_states = self.experts(
             hidden_states=hidden_states,
             router_logits=router_logits,
             is_prefill=is_prefill,
             top_k=CustomDeepseekV2MoE.top_k,
             enable_force_load_balance=enable_force_load_balance,
-        ) * self.routed_scaling_factor
+            **kwargs)
+
+        if multistream:
+            hidden_states, shared_output = hidden_states
+
+        hidden_states = hidden_states * self.routed_scaling_factor
 
         if self.tp_size > 1:
             if self.torchair_graph_enabled:
@@ -288,7 +304,8 @@ class CustomDeepseekV2MoE(nn.Module):
                     hidden_states = hidden_states[:-num_padding_tokens]
 
         if self.n_shared_experts is not None:
-            shared_output = self.shared_experts(old_hidden_states)
+            if not multistream:
+                shared_output = self.shared_experts(old_hidden_states)
 
         if shared_output is not None:
             hidden_states = hidden_states + shared_output