dt-bindings: thermal: Add binding document for Mediatek thermal controller

This adds the device tree binding documentation for the mediatek thermal
controller found on Mediatek MT2712.
Signed-off-by: Louis Yu <louis.yu@mediatek.com>
Reviewed-by: Dawei Chien <dawei.chien@mediatek.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>

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

@@ -11,6 +11,7 @@ Required properties:
 - compatible:
   - "mediatek,mt8173-thermal" : For MT8173 family of SoCs
   - "mediatek,mt2701-thermal" : For MT2701 family of SoCs
+  - "mediatek,mt2712-thermal" : For MT2712 family of SoCs
 - reg: Address range of the thermal controller
 - interrupts: IRQ for the thermal controller
 - clocks, clock-names: Clocks needed for the thermal controller. required