[seL4] Accessing GPIOs on Raspberry Pi

Hello All, I am new to seL4. I want to use seL4 in my project. As a starting point, I have compiled seL4 for Raspberry pi 3. As a next step, I have been trying to access GPIOs on Raspberry Pi. I used gpio.h from util_libs/libplatsupport/arch_include/arm/platsupport. I could not find any gpio.c for Rpi3/bcm2837 platform. When I compile the code, I am getting error: undefined reference to `gpio_sys_init'. Is there any support for GPIO access already available for Raspberry Pi? Could you please provide me guidance on how I can work with the Raspberry Pi GPIOs with seL4. Best Regards Zohra