Migrate avg pooling

src/backends/cuda/layers/avg_pooling.cu

@@ -0,0 +1,45 @@
+#include "avg_pooling.hpp"
+#include "cuda_helper.cuh"
+#include "pooling.cuh"
+
+using namespace CUDANet::Layers;
+
+void AvgPooling2d::initCUDA() {
+    d_output = nullptr;
+    CUDA_CHECK(cudaMalloc(
+        (void**)&d_output,
+        sizeof(float) * outputSize.first * outputSize.second * nChannels
+    ));
+}
+
+void AvgPooling2d::delCUDA() {
+    cudaFree(d_output);
+}
+
+float* AvgPooling2d::forwardCUDA(const float* d_input) {
+    dim3 block(8, 8, 8);
+    dim3 grid(
+        (outputSize.first + block.x - 1) / block.x,
+        (outputSize.second + block.y - 1) / block.y,
+        (nChannels + block.z - 1) / block.z
+    );
+
+    Kernels::avg_pooling<<<grid, block>>>(
+        d_input, d_output, inputSize, outputSize, nChannels, poolingSize,
+        stride, padding
+    );
+    CUDA_CHECK(cudaGetLastError());
+
+    activation->activate(d_output);
+    CUDA_CHECK(cudaDeviceSynchronize());
+
+    return d_output;
+}
+
+void AdaptiveAvgPooling2d::initCUDA() {
+    cudaFree(d_output);
+    cudaMalloc(
+        (void**)&d_output,
+        sizeof(float) * outputSize.first * outputSize.second * nChannels
+    );
+}