[Attention] Add ROCM_AITER_MLA_SPARSE to attention backend registry (#29103)

Signed-off-by: Matthew Bonanni <mbonanni@redhat.com>

vllm/attention/backends/registry.py

@@ -52,6 +52,9 @@ class AttentionBackendEnum(Enum, metaclass=_AttentionBackendEnumMeta):
     ROCM_AITER_FA = (
         "vllm.v1.attention.backends.rocm_aiter_fa.AiterFlashAttentionBackend"
     )
+    ROCM_AITER_MLA_SPARSE = (
+        "vllm.v1.attention.backends.mla.rocm_aiter_mla_sparse.ROCMAiterMLASparseBackend"
+    )
     TORCH_SDPA = ""  # this tag is only used for ViT
     FLASHINFER = "vllm.v1.attention.backends.flashinfer.FlashInferBackend"
     FLASHINFER_MLA = (

vllm/platforms/rocm.py

@@ -233,10 +233,7 @@ class RocmPlatform(Platform):
                 "Sparse MLA backend on ROCm only supports block size 1 for now."
             )
             logger.info_once("Using Sparse MLA backend on V1 engine.")
-            return (
-                "vllm.v1.attention.backends.mla.rocm_aiter_mla_sparse."
-                "ROCMAiterMLASparseBackend"
-            )
+            return AttentionBackendEnum.ROCM_AITER_MLA_SPARSE.get_path()
 
         if use_mla:
             if selected_backend is None: