Replace naive omatcopy_rt with 4x4 blocked implementation
Replace naive omatcopy_rt with 4x4 blocked implementation

as suggested by MigMuc in issue 2532
xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS