Rename files in sgl kernel to avoid nested folder structure (#4213)

Co-authored-by: zhyncs <me@zhyncs.com>

sgl-kernel/csrc/elementwise/fused_add_rms_norm_kernel.cu

@@ -0,0 +1,55 @@
+/* Copyright 2025 SGLang Team. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+==============================================================================*/
+
+#include <ATen/cuda/CUDAContext.h>
+
+#include <flashinfer/norm.cuh>
+
+#include "utils.h"
+
+using namespace flashinfer;
+
+void sgl_fused_add_rmsnorm(torch::Tensor input, torch::Tensor residual, torch::Tensor weight, double eps) {
+  CHECK_INPUT(input);
+  CHECK_INPUT(residual);
+  CHECK_INPUT(weight);
+  auto device = input.device();
+  CHECK_EQ(residual.device(), device);
+  CHECK_EQ(weight.device(), device);
+  CHECK_DIM(2, input);     // input: (batch_size, hidden_size)
+  CHECK_DIM(2, residual);  // residual: (batch_size, hidden_size)
+  CHECK_DIM(1, weight);    // weight: (hidden_size)
+  CHECK_EQ(input.size(0), residual.size(0));
+  CHECK_EQ(input.size(1), residual.size(1));
+  CHECK_EQ(input.size(1), weight.size(0));
+  unsigned int batch_size = input.size(0);
+  unsigned int hidden_size = input.size(1);
+
+  cudaStream_t torch_current_stream = at::cuda::getCurrentCUDAStream();
+  // support float16, bfloat16 and float32
+  DISPATCH_PYTORCH_DTYPE_TO_CTYPE_FLOAT_FP16(input.scalar_type(), c_type, [&] {
+    cudaError_t status = norm::FusedAddRMSNorm(
+        static_cast<c_type*>(input.data_ptr()),
+        static_cast<c_type*>(residual.data_ptr()),
+        static_cast<c_type*>(weight.data_ptr()),
+        batch_size,
+        hidden_size,
+        eps,
+        torch_current_stream);
+    TORCH_CHECK(
+        status == cudaSuccess, "FusedAddRMSNorm failed with error code " + std::string(cudaGetErrorString(status)));
+    return true;
+  });
+}