[Attention] Refactor AttentionMetadata Preparation for Encoder-only Models (#23154)

Signed-off-by: Chen Zhang <zhangch99@outlook.com>

vllm/model_executor/models/llama.py

@@ -31,6 +31,7 @@ from torch import nn
 from transformers import LlamaConfig
 
 from vllm.attention import Attention, AttentionType
+from vllm.attention.layers.encoder_only_attention import EncoderOnlyAttention
 from vllm.compilation.decorators import support_torch_compile
 from vllm.config import CacheConfig, VllmConfig
 from vllm.distributed import get_pp_group, get_tensor_model_parallel_world_size
@@ -173,7 +174,10 @@ class LlamaAttention(nn.Module):
             if is_sliding:
                 sliding_window = config.sliding_window
 
-        self.attn = Attention(
+        attn_cls = (EncoderOnlyAttention
+                    if attn_type == AttentionType.ENCODER_ONLY else Attention)
+
+        self.attn = attn_cls(
             self.num_heads,
             self.head_dim,
             self.scaling,