arm64: dts: zte: add tvenc device for zx296718

It adds VOU tvenc device in zx296718.dtsi, so that boards with TV
connector can enable the support by changing 'status' in board DTS file.
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm64/boot/dts/zte/zx296718.dtsi

@@ -398,6 +398,13 @@ hdmi: hdmi@c000 {
 				#sound-dai-cells = <0>;
 				status = "disabled";
 			};
+
+			tvenc: tvenc@2000 {
+				compatible = "zte,zx296718-tvenc";
+				reg = <0x2000 0x1000>;
+				zte,tvenc-power-control = <&sysctrl 0x170 0x10>;
+				status = "disabled";
+			};
 		};
 
 		topcrm: clock-controller@1461000 {