Hi,
You should use .rpd file which is supported in ASx1/x4 configuration scheme. Since RSU is supported in ASx1/x4 configuration scheme, then you should be using .rpd file. The .rpd file is a binary file for EPCQ/EPCS devices containing a binary bitstream of configuration data for FPGAs that support Active Serial configuration. Thus the .rpd file is equivalent to the contents in .jic and .pof file without the header. You can refer to the following solution link:
https://www.altera.com/support/support-resources/knowledge-base/solutions/rd11182013_802.html