You can use either EEPROM or external master to supply descriptors to SX2.
In case if you use EEPROM then the format should be as mentioend in the 'Boot Methods' section of the SX2 data sheet.
If you use external master to load the descriptors then the master should write into the 500 bytes of descriptor RAM. The writing should be according to the "Command Protocol" mentioned in the data sheet.
Also refer to "Enumeration" section in the data sheet for clear explanation.
Let us know if there are any queries after going through the above mentioned scetions.
For your reference below is the link for SX2 datasheet: