EMLIB provides a macro called RAMFUNC, so you can use it. Due to the RAM size, it is not realistic to deploy all the user code in RAM, so I think the operation will be to select only the necessary functions and place them in RAM.

For more information about RAMFUNC, see Simplicity Studio's Gecko HAL and Driver API Reference. "Gecko HAL and Driver API Reference" for Gecko SDK 5.4 (latest version as of May 2018) is available on SiliconLabs website You can see it though.

Also, there is a code description example using RAMFUNC on the Silicon Labs community site , so please check that as well.