dts: nxp2160ardb: add op-tee node

A defconfig is added on lx2160ardb which allows UEFI variable management
via OP-TEE. Enable the the node in the relevant DTS file.
Signed-off-by: NIlias Apalodimas <ilias.apalodimas@linaro.org>

arch/arm/dts/fsl-lx2160a.dtsi

@@ -428,4 +428,10 @@
 		#size-cells = <0>;
 		status = "disabled";
 	};
+	firmware {
+		optee {
+			compatible = "linaro,optee-tz";
+			method = "smc";
+		};
+	};
 };