[Feature] support eager mode in model runner v2 (#5210)

### What this PR does / why we need it?
#5051 only implement a basic framework for model runner v2, but there
are still some bugs for e2e functionality, this PR aim to enable basic
functionality.
model runner v2 plans:
https://github.com/vllm-project/vllm-ascend/issues/5208

- vLLM version: release/v0.13.0
- vLLM main:
ad32e3e19c
---------
Signed-off-by: Ronald1995 <ronaldautomobile@163.com>

vllm_ascend/attention/mla_v1.py

@@ -5,6 +5,7 @@ from typing import (TYPE_CHECKING, ClassVar, NamedTuple, Optional, Tuple, Type,
 import numpy as np
 import torch
 import torch_npu
+import vllm.envs as envs_vllm
 from vllm.attention.backends.abstract import AttentionBackend, MLAAttentionImpl
 from vllm.attention.backends.utils import PAD_SLOT_ID
 from vllm.config import VllmConfig, get_current_vllm_config
@@ -53,7 +54,10 @@ class AscendMLABackend(AttentionBackend):
 
     @staticmethod
     def get_name() -> str:
-        return "ASCEND_MLA"
+        # HACK(Ronald1995): vllm `initialize_kv_cache` method in model runner v2 make
+        # attention name assertion, we just set name to FLASH_ATTN to avoid assertion error.
+        # rectify this when vllm disable the assertion.
+        return "ASCEND_MLA" if not envs_vllm.VLLM_USE_V2_MODEL_RUNNER else "FLASH_ATTN"
 
     @staticmethod
     def get_builder_cls():