dt-bindings: gpu: mali-utgard: add mediatek, mt7623-mali compatible

The MediaTek MT7623 SoC contains a Mali-450, so add a compatible for it
and define its own vendor-specific properties.

Signed-off-by: Sean Wang <[e-mail]>
Signed-off-by: Ryder Lee <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/e[e-mail]
[mb: move to yaml file]
Signed-off-by: Matthias Brugger <[e-mail]>

Documentation/devicetree/bindings/gpu/arm,mali-utgard.yaml

···
               - amlogic,meson-gxbb-mali
               - amlogic,meson-gxl-mali
               - hisilicon,hi6220-mali
+              - mediatek,mt7623-mali
               - rockchip,rk3328-mali
           - const: arm,mali-450
 
···
               - amlogic,meson8-mali
               - amlogic,meson8b-mali
               - hisilicon,hi6220-mali
+              - mediatek,mt7623-mali
               - rockchip,rk3036-mali
               - rockchip,rk3066-mali
               - rockchip,rk3188-mali