tests: drivers: audio: add dmic API test

Add DMIC API test, intended to verify DMIC drivers are functioning
correctly within the DMIC API.

The test verifies the following:
- Mono channel audio
- Stereo channel audio
- Using maximum number of channels supported by DMIC IP
- Pausing/restarting channels
- Checks to make sure invalid channel maps are rejected by the DMIC.

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>