RF_GPIO0/1, which is the GPIO of the wireless IC, is connected to the MCU's PRS (Peripheral Reflex System) input and is not directly connected to an external pin. RPS output of MCU is connected to PA0/PA1. In other words, RF_GPIO0/1 are “indirectly” connected to PA0/PA1.
Therefore, if you want to output RF_GPIO0/1 externally, you need to set not only RF_GPIO0/1 but also RPS setting and pin setting of MCU.
Please refer to 3.1.29 of the datasheet for detailed explanation and sample code.
Also, check out the Silicon Labs community site.