[Model][Mamba] Add selector for mamba attention backend and make it pluggable for other device (#26487)

Signed-off-by: shen-shanshan <467638484@qq.com>

vllm/model_executor/layers/mamba/mamba_mixer.py

@@ -1,10 +1,7 @@
 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
-from typing import TYPE_CHECKING, NamedTuple
-
-if TYPE_CHECKING:
-    from vllm.attention.backends.abstract import AttentionBackend
+from typing import NamedTuple
 
 import torch
 from torch import nn
@@ -452,11 +449,6 @@ class MambaMixer(MambaBase, CustomOp):
     def mamba_type(self) -> str:
         return "mamba1"
 
-    def get_attn_backend(self) -> type["AttentionBackend"]:
-        from vllm.v1.attention.backends.mamba1_attn import Mamba1AttentionBackend
-
-        return Mamba1AttentionBackend
-
     def _time_proj_bias(self) -> torch.Tensor | None:
         if hasattr(self.dt_proj, "bias") and self.dt_proj.bias is not None:
             return self.dt_proj.bias.float()