You don't want to do that! You'd configure the pin as output and make it high to provide power to the GPS receiver, but microcontrollers I/Os can only supply limited current, 25mA for the STM32F205xx (page 62 of the datasheet), which will be too low for powering a GPS receiver. (This receiver, mentioned in a recent question, needs 50mA.)
Use the I/O pin to drive a PNP transistor which will supply the required current.
Note that using a PNP inverses your logic: a logic low will turn the receiver on.