mark llama4 as not supported with fa2 (#37416)

Author: winglian

src/transformers/models/llama4/modeling_llama4.py

@@ -490,7 +490,7 @@ class Llama4PreTrainedModel(PreTrainedModel):
     config_class = Llama4Config
     supports_gradient_checkpointing = True
     _skip_keys_device_placement = ["past_key_values"]
-    _supports_flash_attn_2 = True
+    _supports_flash_attn_2 = False
     _supports_sdpa = True
     _supports_flex_attn = True
     _supports_cache_class = True