ARM: tegra: colibri_t20: iris: add missing aliases

Add rtc0 being the ultra low-power I2C one as found on the carrier board
and the 3rd UART being NVIDIA's UARTB.
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

arch/arm/boot/dts/tegra20-colibri-iris.dts

@@ -8,10 +8,12 @@ / {
 	compatible = "toradex,iris", "toradex,colibri_t20-512", "nvidia,tegra20";
 
 	aliases {
-		rtc0 = "/i2c@7000d000/tps6586x@34";
-		rtc1 = "/rtc@7000e000";
+		rtc0 = "/i2c@7000c000/rtc@68";
+		rtc1 = "/i2c@7000d000/tps6586x@34";
+		rtc2 = "/rtc@7000e000";
 		serial0 = &uarta;
 		serial1 = &uartd;
+		serial2 = &uartb;
 	};
 
 	chosen {