Add devicetree bindings for MediaTek MT7622 thermal controller

Changes v1 -> v2: add tag from Rob
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Shunli Wang <shunli.wang@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>