OCL: Optimize OpenCL reduce function

check_regression=*Reduce*
test_modules=core

For reducing into column was added intermediate buffer (with size 32 x src_height).
Now reducing process contains two step. First every row reduces with step 32 into the corresponding row of the intermediate buffer and then reduce this buffer into destination.

http://ocl.itseez.com/intel/export/perf/pr/2778/report/