[Sampler] Support returning all logprobs or logits (#21792)

Signed-off-by: 22quinn <33176974+22quinn@users.noreply.github.com>

vllm/v1/engine/processor.py

@@ -65,8 +65,11 @@ class Processor:
         params: SamplingParams,
     ) -> None:
         max_logprobs = self.model_config.max_logprobs
+        if max_logprobs == -1:
+            return
         # Validate sample logprobs.
-        if params.logprobs and params.logprobs > max_logprobs:
+        if params.logprobs and (params.logprobs == -1
+                                or params.logprobs > max_logprobs):
             raise ValueError(
                 f"Requested sample logprobs of {params.logprobs}, "
                 f"which is greater than max allowed: {max_logprobs}")