dt-bindings: mali-midgard: Allow dma-coherent

Add the boolean dma-coherent property to the list of allowed properties,
since some boards (Arm Juno) integrate the GPU this way.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Rob Herring <robh@kernel.org>

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

@@ -87,6 +87,8 @@ properties:
   "#cooling-cells":
     const: 2
 
+  dma-coherent: true
+
 required:
   - compatible
   - reg