docs: fix build without opencv_contrib (avoid links to CUDA modules)

doc/tutorials/gpu/gpu-basics-similarity/gpu_basics_similarity.markdown

@@ -1,3 +1,4 @@
+@cond CUDA_MODULES
 Similarity check (PNSR and SSIM) on the GPU {#tutorial_gpu_basics_similarity}
 ===========================================
 @todo update this tutorial
@@ -204,3 +205,4 @@ It may be just the improvement needed for your application to work. You may obse
 instance of this on the [YouTube here](https://www.youtube.com/watch?v=3_ESXmFlnvY).
 
 @youtube{3_ESXmFlnvY}
+@endcond

doc/tutorials/gpu/gpu-thrust-interop/gpu_thrust_interop.markdown

@@ -1,3 +1,4 @@
+@cond CUDA_MODULES
 Using a cv::cuda::GpuMat with thrust {#tutorial_gpu_thrust_interop}
 ===========================================
 
@@ -68,3 +69,4 @@ Next we will determine how many values are greater than 0 by using thrust::count
 
 We will use those results to create an output buffer for storing the copied values, we will then use copy_if with the same predicate to populate the output buffer.
 Lastly we will download the values into a CPU mat for viewing.
+@endcond

doc/tutorials/gpu/table_of_content_gpu.markdown

@@ -1,3 +1,4 @@
+@cond CUDA_MODULES
 GPU-Accelerated Computer Vision (cuda module) {#tutorial_table_of_content_gpu}
 =============================================
 
@@ -20,3 +21,4 @@ run the OpenCV algorithms.
 
     This tutorial will show you how to wrap a GpuMat into a thrust iterator in order to be able to
     use the functions in the thrust library.
+@endcond