Hello Saito San,
S25F512T family is in the road map and we do not yet have the preliminary datasheet ready for this part . So we can not comment on the D8h meaning in S25FL512T now.
Regarding the identification of SPI we recommend you to read Device ID to know the density and family to which it belongs and choose sub routine accordingly. Device ID will be useful because it is different for different densities and different families.