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

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

tests/models/multimodal/generation/test_vit_backend_functionality.py

@@ -14,10 +14,10 @@ import pytest
 from transformers import AutoProcessor
 
 from vllm import LLM, EngineArgs, SamplingParams
-from vllm.attention.backends.registry import AttentionBackendEnum
 from vllm.multimodal.utils import encode_image_url
 from vllm.multimodal.video import sample_frames_from_video
 from vllm.platforms import current_platform
+from vllm.v1.attention.backends.registry import AttentionBackendEnum
 
 from ....utils import create_new_process_for_each_test
 from ...utils import dummy_hf_overrides