tilelink2 ToAXI4: don't interlock R+W for non-FIFO masters (#822)

idCount <= 1 implies that no more than one transaction can be inflight,
so there is no need to interlock R+W. However, when stripBits > 0, it is
possible for a non-FIFO master to have > 1 idCount. In this case, we
also don't need to interlock R+W.