It is not about number of sticks, but about number of ranks. SODIMM may have 2 ranks (each rank has its own Sx# pin), which is the same as if you had 2 single-rank SODIMMs (except for SPD, of course). Regular DIMM may have 4 ranks. So, if your chip only supports 2 ranks, there's no need to install two sockets. One SODIMM will do just as well.