OCL: optimization for ocl_gemm

Added OpenCL kernel for gemm
optimization:
* local buffer
* use vectors

Performance report:
http://ocl.itseez.com/intel/export/perf/pr/3159/report/

check_regression=OCL*Gemm*
test_filter=OCL*Gemm*
test_modules=core
build_examples=OFF
I think double bracket are unnecessary.