dt-bindings: sound: add Arm PL041 AACI DT schema

The Arm PrimeCell Advanced Audio CODEC Interface (AACI aka PL041) is
a peripheral that provides communication with an audio CODEC.

Add a simple DT schema binding for it, so that DTs can be validated
automatically.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220506140533.3566431-5-andre.przywara@arm.com