ASoC: dt-bindings: Document Microchip's PDMC

Add DT bindings for the new Microchip PDMC embedded in sama7g5 SoCs.

Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20220307122202.2251639-3-codrin.ciubotariu@microchip.com


Signed-off-by: Mark Brown <broonie@kernel.org>