Unified CUDA and OpenCL fields in gmx_gpu_info_t

1. hw_info.h - Replaced cuda_dev and ocl_dev  fields by gpu_dev
2. hw_info.h - Removed #include "config.h"
3. cuda_dev_info becomes gpu_info
4. ocl_dev_info becomes gpu_info
5. Moved OCL specific data structures to oclutils.h
6. Moved OCL specific functions (data transfer) to oclutils.cpp