Activate exp. headers I2C interfaces BBx15


I’m having trouble accessing the I2C5 interface that is available (according to schematic) in exp. header P18. It does not seem to be active as default on a clean debian BBx15 image as far as I can see but I’m very much a novice in this field.
Is it possible to access the I2C5 interface from the P18 header and if it is, what do I have to do to get it working?