Fused two elementwise kernels for k_nope and k_pe concat (#14862)

1 TC failure to check, but irrelevant to this code change

python/sglang/srt/models/deepseek_v2.py

@@ -2698,6 +2698,9 @@ class DeepseekV2AttentionMLA(nn.Module):
                 attn_dtype = k_nope.dtype
             k = k_nope.new_empty(*k_shape, dtype=attn_dtype)
             concat_and_cast_mha_k_triton(k, k_nope, k_pe)
+        elif _is_hip and self.current_attention_backend == "aiter":
+            k = k_nope.new_empty(*k_shape)
+            concat_and_cast_mha_k_triton(k, k_nope, k_pe)
         else:
             k = k_nope.new_empty(*k_shape)
             k[..., : self.qk_nope_head_dim] = k_nope