[stm32] actuators_pwm: replace set_servo_gpio with gpio_setup_pin_af

- AFIO remap in board file
- gpio_setup_pin_af with uint32_t for af
- remove PWM_SERVO_x_RCC

Confirmed to fix actuators_pwm on LisaL, please also test on LisaM and F4 boards...
That is not related to this pull, but can you be a bit more specific? gpio_get is a function from libopencm3...