ARM: dts: rockchip: enable ARM Mali GPU on rk3288-tinker

Add reference to the Mali GPU device tree node on rk3288-tinker.
Tested on Tinker board.
Signed-off-by: Jacob Chen <jacob-chen@iotwrt.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm/boot/dts/rk3288-tinker.dts

@@ -156,6 +156,11 @@ &gmac {
 	status = "ok";
 };
 
+&gpu {
+	mali-supply = <&vdd_gpu>;
+	status = "okay";
+};
+
 &hdmi {
 	ddc-i2c-bus = <&i2c5>;
 	status = "okay";