Add the period cell to GD32 PWM compatible and update all boards accordingly. A period of 20 ms (50 Hz) has been set for all PWM LEDs. Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
add gd32vf103c_starter board. Signed-off-by: YuLong Yao <feilongphone@gmail.com>