arm: dt: hikey: Add optee node

Sync with 14e21cb8f811 ("arm64: dt: hikey: Add optee node"
from Linux kernel.
Reviewed-by: NSimon Glass <sjg@chromium.org>
Signed-off-by: NJens Wiklander <jens.wiklander@linaro.org>

arch/arm/dts/hi6220-hikey.dts

@@ -31,6 +31,13 @@
 		device_type = "memory";
 		reg = <0x0 0x0 0x0 0x40000000>;
 	};
+
+	firmware {
+		optee {
+			compatible = "linaro,optee-tz";
+			method = "smc";
+		};
+	};
 };
 
 &uart2 {