[Kernel] Add FP8 support with FlashMLA backend (#22668)

Signed-off-by: Matthew Bonanni <mbonanni001@gmail.com>

vllm/engine/arg_utils.py

@@ -1445,10 +1445,9 @@ class EngineArgs:
                                recommend_to_remove=False)
             return False
 
-        # No Fp8 KV cache so far.
         if self.kv_cache_dtype != "auto":
             supported = current_platform.is_kv_cache_dtype_supported(
-                self.kv_cache_dtype)
+                self.kv_cache_dtype, model_config)
             if not supported:
                 _raise_or_fallback(feature_name="--kv-cache-dtype",
                                    recommend_to_remove=False)