T-API: minor optimization of cv::warpAffine

**Brief description:**
* Increased number of rows per each work-item
* Used build-in functions (mad24, fma)

**Performance report:**
http://ocl.itseez.com/intel/export/perf/pr/2823/report/

check_regression=*OCL*WarpAffine*
test_filter=*OCL*WarpAffine*
test_modules=imgproc
build_examples=OFF