Add mt7986 audio afe document. Signed-off-by: Maso Huang <maso.huang@mediatek.com> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com> Link: https://lore.kernel.org/r/20230817101338.18782-7-maso.huang@mediatek.com Signed-off-by: Mark Brown <broonie@kernel.org>