[VLM] Support caching in merged multi-modal processor (#11396)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

vllm/transformers_utils/processor.py

@@ -1,25 +1,31 @@
 from functools import lru_cache
 from typing import Any, cast
 
+from transformers.processing_utils import ProcessorMixin
+
 
 def get_processor(
     processor_name: str,
     *args: Any,
     trust_remote_code: bool = False,
+    processor_cls: type[ProcessorMixin] = ProcessorMixin,
     **kwargs: Any,
 ):
     """Load a processor for the given model name via HuggingFace."""
     # don't put this import at the top level
     # it will call torch.cuda.device_count()
     from transformers import AutoProcessor
-    from transformers.processing_utils import ProcessorMixin
+
+    processor_factory = (AutoProcessor
+                         if processor_cls == ProcessorMixin else processor_cls)
 
     try:
-        processor = AutoProcessor.from_pretrained(
+        processor = processor_factory.from_pretrained(
             processor_name,
             *args,
             trust_remote_code=trust_remote_code,
-            **kwargs)
+            **kwargs,
+        )
     except ValueError as e:
         # If the error pertains to the processor class not existing or not
         # currently being imported, suggest using the --trust-remote-code flag.