imx: imx8mn_smm_s2/s2pro: Enable TrustZone

When the board was added, enabling tzc380 was left off by
mistake. The optee was tested with the following configuration
in s2pro

+	firmware {
+		optee {
+			compatible = "linaro,optee-tz";
+			method = "smc";
+		};
+	};
+
+	reserved-memory {
+		#address-cells = <2>;
+		#size-cells = <2>;
+		ranges;
+
+		/* 6MiB */
+		optee_core@5f800000 {
+			reg = <0x00 0x5f800000 0x00 0x600000>;
+		};
+
+		/* 2MiB */
+		optee_shm@5fe00000 {
+			reg = <0x00 0x5fe00000 0x00 0x200000>;
+		};
+	};
+

Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>