ARM64: dts: meson-axg: add an 32K alt aoclk

The ao_clk81 in AO domain have two clock source,
one from a 32K alt crystal we name it as ao_alt_clk,
another is the clk81 signal from EE domain.

Acked-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Yixun Lan <yixun.lan@amlogic.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>

arch/arm64/boot/dts/amlogic/meson-axg.dtsi

@@ -108,6 +108,13 @@
 		#clock-cells = <0>;
 	};
 
+	ao_alt_xtal: ao_alt_xtal-clk {
+		compatible = "fixed-clock";
+		clock-frequency = <32000000>;
+		clock-output-names = "ao_alt_xtal";
+		#clock-cells = <0>;
+	};
+
 	soc {
 		compatible = "simple-bus";
 		#address-cells = <2>;