powerpc: t2080rdb: Enable RTC support

The T2080RDB has a ds1339 on i2c0. Add this to the devicetree and enable
the relevant support in the configs.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>

arch/powerpc/dts/t2080rdb.dts

@@ -30,3 +30,11 @@
 		spi-max-frequency = <10000000>; /* input clock */
 	};
 };
+
+&i2c0 {
+	status = "okay";
+	rtc@68 {
+		compatible = "dallas,ds1339";
+		reg = <0x68>;
+	};
+};