PDM control register
| PDMEN | PDM enable  |  
| MICNBR | Number of microphones  |  
| CKEN1 | Clock enable of bitstream clock number 1  |  
| CKEN2 | Clock enable of bitstream clock number 2  |  
| CKEN3 | Clock enable of bitstream clock number 3  |  
| CKEN4 | Clock enable of bitstream clock number 4  |