The PCM5242 is a simple device to layout. Most engineers use a shared common ground for the entire device. GND can be consider AGND and DGND connected.
Good system partitioning should keep digital clock and interface traces away from the differential analog outputs for highest analog performance. This reduces any high speed clock return currents influencing the analog outputs.
Power supply and charge pump decoupling capacitors should be placed as close as possible to the device.
The thermal pad on the underside of the package should be connected to GND.
The top layer should be used for routing signals, whilst the bottom layer can be used for GND.