GitLab

Refine error message when GPU is not detected.

Possible solutions if hardware exists and drivers are already installed:
* nvidia gpus:
  ```sh
  /sbin/modprobe nvidia-uvm
  D=`grep nvidia-uvm /proc/devices | awk '{print $1}'`
  mknod -m 666 /dev/nvidia-uvm c $D 0
  ```

* amd gpus
  ```sh
  modprobe amdgpu
  ```