arm64: dts: r8a7796: Add CAN external clock support

Adds external CAN clock node for r8a7796. This clock can be used as
fCAN clock of CAN and CAN FD controller.

Based on a patch for r8a7795 by Ramesh Shanmugasundaram.
Signed-off-by: NChris Paterson <chris.paterson2@renesas.com>
Reviewed-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Acked-by: NMarc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>

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

@@ -69,6 +69,13 @@
 		clock-frequency = <0>;
 	};
 
+	/* External CAN clock - to be overridden by boards that provide it */
+	can_clk: can {
+		compatible = "fixed-clock";
+		#clock-cells = <0>;
+		clock-frequency = <0>;
+	};
+
 	/* External SCIF clock - to be overridden by boards that provide it */
 	scif_clk: scif {
 		compatible = "fixed-clock";