Add device tree binding documentation for Everest ES8326

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v5 tested by dtschema
Signed-off-by: David Yang <yangxiaohua@everest-semi.com>
Signed-off-by: Zhu Ning <zhuning@everest-semi.com>
Link: https://lore.kernel.org/r/20220816024456.4475-1-zhuning0077@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>