It depends what you mean by a servo. If you mean a "hobby servo" (like they use on radio-controlled cars), then you just need to generate a PWM output. You could do one of them using the hardware PWM, or more of them using software PWM like

http://cq.cx/ladder-forum.pl?action=viewthread&parent=3

If you mean a real servo (where you measure its position somehow, and close the loop with your own controller) then things are more complicated.

Look at the attachment for an example of a PI controller, that adjusts the PWM duty cycle to achieve a programmed setpoint on an analog input.

You could use something like that to do a servo controller yourself (though of course that should be a PD controller, not PI). But it would be simpler to use something like a Gecko drive, and just generate the step and direction signals.