T-API: optimization of cv::remap

**Description:**
* increased number of rows per work-item
* used precomputed bufferof interpolation coefficients
* used `vload2` for `INTER_LINEAR`

**Performance report:**
http://ocl.itseez.com/intel/export/perf/pr/2888/report/

check_regression=*OCL*Remap*
test_modules=imgproc
test_filter=*OCL*Remap*
build_examples=OFF
Why not 
```
 for (int y = y0, y1 = min(dst_rows, y0 + rowsPerWI); y < y1; ++y,
```
as in other kernel (`inrange` for example)?