gen_opencl_kernel: add script to dynamically create OpenCL kernels

Compute tests can be produced by using OpenCL, by calling ocloc.

While this can be part of IGT building system, for now, let's add
a script for such purpose.

Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Acked-by: Kamil Konieczny <kamil.konieczny@linux.intel.com>