T-API: optimized stitching warpers (buildMaps)

check_regression=*OCL*Warper*
test_modules=stitching

* Used the following built-in functions:
  * `sin+cos` are combined into `sincos` function
  * instead of a*b+c `fma` is used
* Increased number of rows that are processed by work-items. 

http://ocl.itseez.com/intel/export/perf/pr/2761/report/