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
byte read is very inefficient. could you try to unroll this loop by 4 and use uchar4 or vload4?