OCL: Optimize OpenCL version of StereoBM function

1. Fix problems on NVidia devices.
2. Move some arguments to build options
3. Refactoring some code.

http://ocl.itseez.com/intel/export/perf/pr/3284/report/

check_regression=*OCL*StereoBM*
test_filter=*OCL*StereoBM*
test_modules=calib3d
build_examples=OFF
@krodyush I'm not sure that another other approach will give a significant performance improvement. In any cases we have problems with a difficulity of the windows sum computation and local memory limitation (current approach tries to minimize it). Of cause, may be there is a better algorithm, but it's realy not a trivial problem.