[Bugfix] Avoid import AttentionMetadata explicitly in Mllama (#10593)

Signed-off-by: Isotr0py <2037008807@qq.com>

vllm/platforms/openvino.py

@@ -1,7 +1,5 @@
 from typing import TYPE_CHECKING
 
-import openvino as ov
-import openvino.properties.hint as hints
 import torch
 
 import vllm.envs as envs
@@ -16,6 +14,12 @@ else:
 
 logger = init_logger(__name__)
 
+try:
+    import openvino as ov
+    import openvino.properties.hint as hints
+except ImportError as e:
+    logger.warning("Failed to import OpenVINO with %r", e)
+
 
 class OpenVinoPlatform(Platform):
     _enum = PlatformEnum.OPENVINO