arm64: dts: r8a7796: Add external audio clocks

Add the external audio clocks as zero Hz fixed-frequency clocks.
Boards that provide these clocks should override them.

Based on commit 623197b9 ("arm64: renesas: r8a7795: Sound SSI
PIO support").
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm64/boot/dts/renesas/r8a7796.dtsi

@@ -120,6 +120,29 @@ extalr_clk: extalr {
 		clock-frequency = <0>;
 	};
 
+	/*
+	 * The external audio clocks are configured as 0 Hz fixed frequency
+	 * clocks by default.
+	 * Boards that provide audio clocks should override them.
+	 */
+	audio_clk_a: audio_clk_a {
+		compatible = "fixed-clock";
+		#clock-cells = <0>;
+		clock-frequency = <0>;
+	};
+
+	audio_clk_b: audio_clk_b {
+		compatible = "fixed-clock";
+		#clock-cells = <0>;
+		clock-frequency = <0>;
+	};
+
+	audio_clk_c: audio_clk_c {
+		compatible = "fixed-clock";
+		#clock-cells = <0>;
+		clock-frequency = <0>;
+	};
+
 	/* External CAN clock - to be overridden by boards that provide it */
 	can_clk: can {
 		compatible = "fixed-clock";