To integrate your board into LimeSuite GUI/API, at first you need to create new or modify existing connection. There is already one SPI connection for RPi that was created for LimeNet-Micro, so it may give some hints https://github.com/myriadrf/LimeSuite/tree/master/src/ConnectionSPI .
Implementing device enumeration, open/close, and LMS SPI read/write functionality in connection will probably be enough to change LMS chip settings from LimeSuiteGUI. However, there will be errors when LimeSuite attempts to configure FPGA (or other on-board stuff ). To deal with board specifics, you will need to create new or modify existing device class (lime::LMS7_Device or derived).