[1/N][Attention] Restructure attention: move files (#31916)

Signed-off-by: Matthew Bonanni <mbonanni@redhat.com>

vllm/model_executor/models/mimo_v2_flash.py

@@ -6,7 +6,6 @@ from itertools import islice
 import torch
 from torch import nn
 
-from vllm.attention.backends.abstract import AttentionType
 from vllm.attention.layer import Attention
 from vllm.config import (
     CacheConfig,
@@ -43,6 +42,7 @@ from vllm.model_executor.model_loader.weight_utils import (
 )
 from vllm.model_executor.models.utils import sequence_parallel_chunk
 from vllm.sequence import IntermediateTensors
+from vllm.v1.attention.backend import AttentionType
 
 from .interfaces import MixtureOfExperts, SupportsPP
 from .utils import (