ASoC: dsp: mediatek: add mt8195 dsp document

This patch adds mt8195 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: yc.hung <yc.hung@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220106064847.15588-1-yc.hung@mediatek.com


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