the `ocl` module code always makes copying when converting CPU memory to cl_mem; it includes C3->C4 conversion, so kernels can rely on the dummy 4th channel;
in `master' we move OCL-optimized code from `ocl` to the appropriate OCV modules and enable transparent calls to it from OCV API; there we use zero-copy for RAM->cl_mem if possible, so we disable C3 Mat-s processing via OCL if the kernel rely on the dummy 4th channel; it means  such code will have to be refactored before been used for C3 Mat-s.