Add support for OpenCL 1.1 C and C++ API

By default OpenCL is configured for NVIDIA CUDA. <PKG>/include and
<PKG>/lib64 are symlinks, which can me modified to point to
alternative implementation.

`opencl` and `opencl-cpp` are optional toolfiles and must be loaded
explicitly.

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>