The mic driver has been removed, at the same time, documentation is not particularly clear.
Doesn't see as we have any example in the nRF5 SDK, but you can find this useful:https://devzone.nordicsemi.com/f/nordic-q-a/48933/pdm-example-in-sdk-15-3-0
You can also refer to the product specification on usage of the PDM peripheral hardware. Hopefully this should get you going.
