[Feat][Graph] Support MTP for ACL Graph (#2932)

### What this PR does / why we need it?
This PR depends on the merge of #2707 and has adapted the aclgraph
functionality to support MTP.

### How was this patch tested?


- vLLM version: v0.10.2
- vLLM main:
2b85697031

---------

Signed-off-by: xuyexiong <xuyexiong@huawei.com>

vllm_ascend/spec_decode/mtp_proposer.py

@@ -8,7 +8,7 @@ from torchair import patch_for_hcom
 from vllm.attention.layer import Attention
 from vllm.config import (VllmConfig, get_layers_from_vllm_config,
                          set_current_vllm_config)
-from vllm.forward_context import get_forward_context
+from vllm.forward_context import BatchDescriptor, get_forward_context
 from vllm.model_executor.model_loader import get_model_loader
 from vllm.model_executor.model_loader.utils import (
     process_weights_after_loading, set_default_torch_dtype)
@@ -363,8 +363,14 @@ class MtpProposer(Proposer):
             not self.runner.with_prefill
 
         if is_running_torchair:
+            # Torchair graph mode, padding is same as the main model
             num_input_tokens = self.runner.graph_pad_size
+        elif (self.runner.use_aclgraph
+              and num_tokens <= self.runner.aclgraph_batch_sizes[-1]):
+            # Acl graph mode, add padding to the batch size
+            num_input_tokens = self.vllm_config.pad_for_cudagraph(num_tokens)
         else:
+            # Eager mode, no padding needed
             num_input_tokens = num_tokens
 
         seq_lens = target_positions[last_token_indices] + 1
@@ -410,7 +416,7 @@ class MtpProposer(Proposer):
             # TODO: adapt enable_dbo later
             (num_input_tokens, num_tokens_across_dp, with_prefill,
              _) = self.runner._sync_metadata_across_dp(
-                 num_tokens, self.runner.with_prefill, False)
+                 num_input_tokens, self.runner.with_prefill, False)
         else:
             # torchair mode can reuse self.runner.num_tokens_across_dp
             num_tokens_across_dp = self.runner.num_tokens_across_dp
@@ -418,6 +424,10 @@ class MtpProposer(Proposer):
 
         moe_comm_method = self.runner._select_moe_comm_method(
             num_input_tokens, with_prefill)
+        batch_descriptor = BatchDescriptor(num_tokens=num_input_tokens,
+                                           uniform_decode=False)
+        aclgraph_runtime_mode, batch_descriptor = \
+            self.runner.aclgraph_dispatcher.dispatch(batch_descriptor)
 
         for step in range(self.num_speculative_tokens):
             with set_ascend_forward_context(
@@ -428,6 +438,7 @@ class MtpProposer(Proposer):
                     num_tokens_across_dp=num_tokens_across_dp,
                     reserved_mc2_mask=self.runner.reserved_mc2_mask,
                     moe_comm_method=moe_comm_method,
+                    aclgraph_runtime_mode=aclgraph_runtime_mode,
                     in_profile_run=self.runner.in_profile_run,
                     num_actual_tokens=num_tokens):
                 with ProfileExecuteDuration().capture_async('mtp_forward'):