How to control a 88004 Servo Motor with a Raspberry Pi?
LEGO "Servo Motor" has little to do with a RC servomotor. To drive it, you need to:


Power it at 9V (probably works at 5 volts, but with less torque) through PWR/GND terminals
To move in one direction, send a PWM signal (1200 Hz, 0 to 100% duty cycle) on C1 and keep C2 at GND level. As duty cycle varies, servo motor will move along 7 positions on one side. See this video.
To move in the other direction and reach the 7 other positions, send PWM to C2 and keep C1 at ground level.