dt-bindings: dsp: mediatek: Add mt8186 dsp document

This patch adds mt8186 dsp document. The dsp is used for Sound Open
Firmware driver node. It includes registers, clocks, memory regions,
and mailbox for dsp.

Signed-off-by: Tinghan Shen <tinghan.shen@mediatek.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220622062245.21021-4-tinghan.shen@mediatek.com


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