ARM: dt: tegra trimslice: add RTC I2C device

According to the device's datasheet, it can support an interrupt too.
However, the existing board file doesn't specify an interrupt, and I
don't have the schematics, so I can't add an interrupts property. The
current Linux driver doesn't support anyway.
Signed-off-by: NStephen Warren <swarren@nvidia.com>

arch/arm/boot/dts/tegra-trimslice.dts

@@ -250,6 +250,11 @@
 
 	i2c@7000c500 {
 		clock-frequency = <400000>;
+
+		rtc@56 {
+			compatible = "emmicro,em3027";
+			reg = <0x56>;
+		};
 	};
 
 	i2c@7000d000 {