[Feature][eplb] add verify ep or tp or dp (#21102)

Signed-off-by: rongfu.leng <rongfu.leng@daocloud.io>

vllm/config.py

@@ -2108,6 +2108,15 @@ class ParallelConfig:
                 raise ValueError(
                     "num_redundant_experts must be non-negative, but got "
                     f"{self.num_redundant_experts}.")
+            if not self.enable_expert_parallel:
+                raise ValueError(
+                    "enable_expert_parallel must be True to use EPLB.")
+            if self.tensor_parallel_size * self.data_parallel_size <= 1:
+                raise ValueError(
+                    "EPLB requires tensor_parallel_size or data_parallel_size "
+                    f"to be greater than 1, but got "
+                    f"TP={self.tensor_parallel_size},DP={self.data_parallel_size}."
+                )
         else:
             if self.num_redundant_experts != 0:
                 raise ValueError(