Implementation of BF16 based gemv

1. Add a new API -- sbgemv to support bfloat16 based gemv
2. Implement a generic kernel for sbgemv
3. Implement an avx512-bf16 based kernel for sbgemv

Signed-off-by: Chen, Guobing <guobing.chen@intel.com>

interface/gemv.c

@@ -191,7 +191,6 @@ void CNAME(enum CBLAS_ORDER order,
   }
 
 #endif
-  //printf("m=%d, n=%d, trans=%d, incx=%d, incy=%d, alpha=%f, beta=%f\n", m, n, trans, incx, incy, alpha, beta);
   if ((m==0) || (n==0)) return;
 
   lenx = n;