OCL: stitching warpers

- Attempt to optimize buildMaps kernels in case rowsPerWI > 1.
- Fixed call of PlaneWarper kernel

**Performance report**
http://ocl.itseez.com/intel/export/perf/pr/3359/report/

check_regression=*OCL*Warper*
test_filter=*OCL*Warper*
test_modules=stitching
build_examples=OFF
I think may be we create something like:
```
        float3 a = (float3)(ck_rinv[0], ck_rinv[3], ck_rinv[6]) * (float3)x_;
        float3 b = (float3)(ck_rinv[1], ck_rinv[4], ck_rinv[7]);
        float3 c = (float3)(ck_rinv[2], ck_rinv[5], ck_rinv[8]) * (float3)ct1;
```
before `for` and use it as:
```
            float3 res = a + mad(b, y_, c);
            res.x /= res.z;
            res.y /= res.z;

            xmap[0] = res.x;
            ymap[0] = res.y;
```
And i worry about `z == 0`, we check this in two over kernels.