You can not power any servos from the Pis GPIO.
To attempt to do so will endanger and possibly destroy your Pi.
The Pi's GPIO can only supply about 20mA in current (far too little to power a servo) and should NEVER be directly connected to an inductive load like a motor.
You can't power a servo with a GPIO but you can supply the control signal from a GPIO (the control signal is the 50 Hz stream of pulses used to position the servo).
The Pi's expansion header has two 5V pins. These may be used to power a few servos depending on the following circumstances.
- The amount of spare power (cuurent) available from the 5V pins. This might be nothing to a couple of amps depending on the Pi model and the power supply.
- The power requirement of the servos under no-load. See the servo datasheet.
- The power requirement of the servos under heavy load to stall conditions. See the servo datasheet but be aware this can easily be several amps.
If the 5V pins are overloaded the Pi will crash. This in itself is unlikely to damage the Pi but may corrupt the SD card.