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
```
#if NO_MULT
int ie = min(LOCAL_SIZE, n - p * LOCAL_SIZE);
#else
int ie = LOCAL_SIZE;
#endif
for (int i = 0; i < ie; i++)
...
```
or
```
#if NO_MULT
int ie = min(LOCAL_SIZE, n - p * LOCAL_SIZE);
for (int i = 0; i < ie; i++)
#else
for (int i = 0; i < LOCAL_SIZE; i++)
#endif
```
will be simplest.