void platform_private_write_led(int index, int state);
platform_private_write_led writes state to the GPIO-controlled LED with index index. platform_private_write_led takes care of inverting state for negative-logic LEDs.
If all platform LEDs are controlled using GPIOs that are accessible using platform_write_digital_pin, a platform implementation of platform_write_led can call platform_private_write_led directly.