science/gromacs: Multiple improvements
- remove dependency on xorg: last xorg utility was retired some time ago
- add HWLOC option and pass cmake argument: hwloc2 is only used when this argument is supplied
- refactor OPENCL option: add OPENCL_NONE, OPENCL_ICD, OPENCL_SYCL options
- refactor SIMD option: use the AUTO value when set
- correct OPENMP option