ARM: dts: meson8b: ec100: enable the RTC

The RTC is always enabled on this board since the battery is already
connected in the factory.
According to the schematics the VCC_RTC regulator (which is either
powered by the internal 3.3V or a battery) is connected to the 0.9V
RTC_VDD input of the SoCs.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>

arch/arm/boot/dts/meson8b-ec100.dts

@@ -88,6 +88,14 @@
 		};
 	};
 
+	rtc32k_xtal: rtc32k-xtal-clk {
+		/* X2 in the schematics */
+		compatible = "fixed-clock";
+		clock-frequency = <32768>;
+		clock-output-names = "RTC32K";
+		#clock-cells = <0>;
+	};
+
 	usb_vbus: regulator-usb-vbus {
 		/*
 		 * Silergy SY6288CCAC-GP 2A Power Distribution Switch.
@@ -347,6 +355,12 @@
 	clock-names = "clkin0";
 };
 
+&rtc {
+	status = "okay";
+	clocks = <&rtc32k_xtal>;
+	vdd-supply = <&vcc_rtc>;
+};
+
 /* exposed through the pin headers labeled "URDUG1" on the top of the PCB */
 &uart_AO {
 	status = "okay";