dt/bindings: display: Add optional property node define for Mali DP500

Add optional property node 'arm,malidp-arqos-value' for the Mali DP500.
This property describe the ARQoS levels of DP500's QoS signaling.
Signed-off-by: Wen He <wen.he_1@nxp.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190910075913.17650-1-wen.he_1@nxp.com

Documentation/devicetree/bindings/display/arm,malidp.txt

@@ -37,6 +37,8 @@ Optional properties:
     Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt)
     to be used for the framebuffer; if not present, the framebuffer may
     be located anywhere in memory.
+  - arm,malidp-arqos-high-level: integer of u32 value describing the ARQoS
+    levels of DP500's QoS signaling.
 
 
 Example:
@@ -54,6 +56,7 @@ Example:
 		clocks = <&oscclk2>, <&fpgaosc0>, <&fpgaosc1>, <&fpgaosc1>;
 		clock-names = "pxlclk", "mclk", "aclk", "pclk";
 		arm,malidp-output-port-lines = /bits/ 8 <8 8 8>;
+		arm,malidp-arqos-high-level = <0xd000d000>;
 		port {
 			dp0_output: endpoint {
 				remote-endpoint = <&tda998x_2_input>;