make OpenCL 1st class-citizen in the build system
At the moment the implementation of the GPU support in the build system is rather NVIDIA/CUDA centric and would require a few tweaks to make OpenCL a first-class citizen -- in particular as we're aiming for i) feature pairty ii) OpenCL for backward-compatibility with older hardware.TODOs
- make GMX_GPU multi-value instead of requiring an additional option to switch OpenCL on
- tweak detection so GMX_GPU_AUTO and related code (see
gmxManageGPU.cmake) is not NVIDIA-centric
- change recommendation message
gmxManageGPU.cmakethat recommends "native GPU acceleration on NVIDIA hardware" with CUDA.