ARM: dts: rockchip: Add #cooling-cells entry for rk3288 GPU

The Mali GPU of the rk3288 can be used as cooling device, add
a #cooling-cells entry for it.
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm/boot/dts/rk3288.dtsi

@@ -1286,6 +1286,7 @@ gpu: gpu@ffa30000 {
 		interrupt-names = "job", "mmu", "gpu";
 		clocks = <&cru ACLK_GPU>;
 		operating-points-v2 = <&gpu_opp_table>;
+		#cooling-cells = <2>; /* min followed by max */
 		power-domains = <&power RK3288_PD_GPU>;
 		status = "disabled";
 	};