[Attention] Refactor FA block_size limitations to hybrid models only (#29084)

Signed-off-by: NickLucche <nlucches@redhat.com>

vllm/v1/attention/backends/triton_attn.py

@@ -154,7 +154,6 @@ class TritonAttentionBackend(AttentionBackend):
         torch.bfloat16,
         torch.float32,
     ]
-    supported_kernel_block_sizes: ClassVar[list[int | MultipleOf]] = [MultipleOf(16)]
     supported_kv_cache_dtypes: ClassVar[list[CacheDType]] = [
         "auto",
         "fp8",
@@ -162,6 +161,10 @@ class TritonAttentionBackend(AttentionBackend):
         "fp8_e5m2",
     ]
 
+    @staticmethod
+    def get_supported_kernel_block_sizes() -> list[int | MultipleOf]:
+        return [MultipleOf(16)]
+
     @staticmethod
     def get_name() -> str:
         return "TRITON_ATTN"