Migrate input layer

src/backends/cuda/layers/input.cu

@@ -0,0 +1,22 @@
+#include "cuda_helper.cuh"
+#include "input.hpp"
+
+using namespace CUDANet::Layers;
+
+void Input::initCUDA() {
+    d_output = nullptr;
+    CUDA_CHECK(cudaMalloc((void**)&d_output, sizeof(float) * inputSize));
+}
+
+void Input::delCUDA() {
+    cudaFree(d_output);
+}
+
+float* Input::forwardCUDA(const float* input) {
+    CUDA_CHECK(cudaMemcpy(
+        d_output, input, sizeof(float) * inputSize, cudaMemcpyHostToDevice
+    ));
+    CUDA_CHECK(cudaDeviceSynchronize());
+
+    return d_output;
+}