These seems like another dumb question. First off, I am aware that the nrf21540DK is the nrf52840 with the FEM tacked on the output.
I know I can select the nrf21530DK/nrf52840 as a build target while creating the Build Configuration, which should give me the appropriate device tree for the FEM connections.
What I want to know are what calls I need to make to modify the RF output power and set FEM.
The following project Link sort of makes some changes on the fly, but I am not sure I see what modifications are needed for the FEM TX/ RX lines. I am guessing they are buried in the nrf52 radio driver.