Splitting SCL and SDA pins
An I2C bus can be connected to many slaves at the same time, since in the I2C protocol every slave has an address.

But, as Majenko wrote in the comments, the library for the PS2 controller doesn't use I2C. The communication with the controller is bit banged, meaning that every part of the communication is done by software. This can be done with every digital pin on the Arduino. In your setup you have to usw the function ps2x.config_gamepad().  In it's parameters you can set the pins that the library will use.