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 The main bottleneck of this algo lies in the fact that CPU algo computes the sum in the window only once with O(n^2) difficulity, on the input image's borders with O(n) and inside the image with O(1). On GPU we can use such sliding sum approach only for a local group. Also I suppose there is a problem with a limitation of local memory and vector registers (too small number of groups can be computed in parallel at the moment).