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 <valentine.barshak@cogentembedded.com>
[geert: Verified schematics]
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Link: https://lore.kernel.org/r/75a66bae21937da1c69e8024ce61b35aad4ac9b8.1620119570.git.geert+renesas@glider.be

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

@@ -73,6 +73,12 @@ memory@48000000 {
 		/* 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 {
@@ -104,6 +110,8 @@ channel0 {
 };
 
 &du {
+	clocks = <&cpg CPG_MOD 724>, <&x1_clk>;
+	clock-names = "du.0", "dclkin.0";
 	status = "okay";
 };