Hi, the MCPS layer is the interface between the driver and the higher level stack (for instance Qorvo FiRa + 802.15.4z binary library).
This interface not is especially documented because it is mainly used by the Qorvo library, but the function names are self explanatory. You can take a look at the DW3000 implementation in dw3000_device.c. If you just want to use the driver without the library, you need to implement only the structures which are used.