[MISC] add support custom_op check (#8557)

Co-authored-by: youkaichao <youkaichao@126.com>

vllm/utils.py

@@ -1245,6 +1245,12 @@ def supports_dynamo() -> bool:
     return base_torch_version >= Version("2.4.0")
 
 
+# Some backends use pytorch version < 2.4.0 which doesn't
+# support `torch.library.custom_op`.
+def supports_custom_op() -> bool:
+    return hasattr(torch.library, "custom_op")
+
+
 class AtomicCounter:
     """An atomic, thread-safe counter"""