arm64: dts: renesas: eagle: Add x1 clock

This adds X1 clock which supplies a frequency of 148.5 MHz.
This clock is connected to the external dot clock input signal.

Signed-off-by: Valentine Barshak <[e-mail]>
[geert: Verified schematics]
Signed-off-by: Geert Uytterhoeven <[e-mail]>
Reviewed-by: Kieran Bingham <[e-mail]>
Reviewed-by: Laurent Pinchart <[e-mail]>
Tested-by: Kieran Bingham <[e-mail]>
Link: https://lore.kernel.org/r/75a66[e-mail]

arch/arm64/boot/dts/renesas/r8a77970-eagle.dts

···
 		/* first 128MB is reserved for secure area. */
 		reg = <0x0 0x48000000 0x0 0x38000000>;
 	};
+
+	x1_clk: x1-clock {
+		compatible = "fixed-clock";
+		#clock-cells = <0>;
+		clock-frequency = <148500000>;
+	};
 };
 
 &avb {
···
 };
 
 &du {
+	clocks = <&cpg CPG_MOD 724>, <&x1_clk>;
+	clock-names = "du.0", "dclkin.0";
 	status = "okay";
 };