ARM: dts: am335x-myirtech: Add an external clock oscillator for CPU RTC

The CPU RTC has an external crystal, so to keep time, let's define
it for devicetree.
Signed-off-by: Alexander Shiyan <eagle.alexander923@gmail.com>
Message-Id: <20220427081914.6773-1-eagle.alexander923@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/boot/dts/am335x-myirtech-myc.dtsi

@@ -27,6 +27,13 @@ memory@80000000 {
 		reg = <0x80000000 0x10000000>;
 	};
 
+	clk32k: clk32k {
+		compatible = "fixed-clock";
+		clock-frequency = <32768>;
+
+		#clock-cells = <0>;
+	};
+
 	vdd_mod: vdd_mod_reg {
 		compatible = "regulator-fixed";
 		regulator-name = "vdd-mod";
@@ -149,6 +156,8 @@ eeprom: eeprom@50 {
 };
 
 &rtc {
+	clocks = <&clk32k>;
+	clock-names = "ext-clk";
 	system-power-controller;
 };