dt-bindings: thermal: mediatek: add compatible string for MT7986 and MT7981 SoC

Document compatible string 'mediatek,mt7986-thermal' for V3 thermal
unit found in MT7986 SoCs.
'mediatek,mt7981-thermal' is also added as it is identical with the
thermal unit of MT7986.
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@kernel.org>

Documentation/devicetree/bindings/thermal/mediatek-thermal.txt

@@ -13,6 +13,8 @@ Required properties:
   - "mediatek,mt2701-thermal" : For MT2701 family of SoCs
   - "mediatek,mt2712-thermal" : For MT2712 family of SoCs
   - "mediatek,mt7622-thermal" : For MT7622 SoC
+  - "mediatek,mt7981-thermal", "mediatek,mt7986-thermal" : For MT7981 SoC
+  - "mediatek,mt7986-thermal" : For MT7986 SoC
   - "mediatek,mt8183-thermal" : For MT8183 family of SoCs
   - "mediatek,mt8516-thermal", "mediatek,mt2701-thermal : For MT8516 family of SoCs
 - reg: Address range of the thermal controller