dt-bindings: thermal: mediatek: Add fallback compatible string for MT7981 and MT8516

The ‘mediatek,mt7981-thermal’ and ‘mediatek,mt8516-thermal’ strings
aren't definied in the driver. Both should have fallback compatible
strings. This commit fixes this issue.

Fixes: 788494b ("dt-bindings: thermal: convert Mediatek Thermal to the json-schema")
Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Rafał Miłecki <rafal@milecki.pl>
Link: https://lore.kernel.org/r/20250712195904.6988-2-olek2@wp.pl
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

Author: abajk

Documentation/devicetree/bindings/thermal/mediatek,thermal.yaml

@@ -20,16 +20,23 @@ allOf:
 
 properties:
   compatible:
-    enum:
-      - mediatek,mt2701-thermal
-      - mediatek,mt2712-thermal
-      - mediatek,mt7622-thermal
-      - mediatek,mt7981-thermal
-      - mediatek,mt7986-thermal
-      - mediatek,mt8173-thermal
-      - mediatek,mt8183-thermal
-      - mediatek,mt8365-thermal
-      - mediatek,mt8516-thermal
+    oneOf:
+      - enum:
+          - mediatek,mt2701-thermal
+          - mediatek,mt2712-thermal
+          - mediatek,mt7622-thermal
+          - mediatek,mt7986-thermal
+          - mediatek,mt8173-thermal
+          - mediatek,mt8183-thermal
+          - mediatek,mt8365-thermal
+      - items:
+          - enum:
+              - mediatek,mt8516-thermal
+          - const: mediatek,mt2701-thermal
+      - items:
+          - enum:
+              - mediatek,mt7981-thermal
+          - const: mediatek,mt7986-thermal
 
   reg:
     maxItems: 1