arm64: dts: renesas: gray-hawk-single: Add second debug serial port

Describe the second debug serial port (CN9800) on the Gray Hawk Single
board, as provided by HSCIF2, including the SCIF_CLK2 external clock
source, and all related pin control.

Based on a patch for Gray Hawk in the BSP by Nghia Nguyen.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/6e1faff6a717cb8344661bafcae5db5dcfb53a90.1709741303.git.geert+renesas@glider.be

arch/arm64/boot/dts/renesas/r8a779h0-gray-hawk-single.dts

@@ -18,6 +18,7 @@ / {
 
 	aliases {
 		serial0 = &hscif0;
+		serial1 = &hscif2;
 		ethernet0 = &avb0;
 	};
 
@@ -90,6 +91,14 @@ &hscif0 {
 	status = "okay";
 };
 
+&hscif2 {
+	pinctrl-0 = <&hscif2_pins>;
+	pinctrl-names = "default";
+
+	uart-has-rtscts;
+	status = "okay";
+};
+
 &i2c0 {
 	pinctrl-0 = <&i2c0_pins>;
 	pinctrl-names = "default";
@@ -144,7 +153,7 @@ &mmc0 {
 };
 
 &pfc {
-	pinctrl-0 = <&scif_clk_pins>;
+	pinctrl-0 = <&scif_clk_pins>, <&scif_clk2_pins>;
 	pinctrl-names = "default";
 
 	avb0_pins: avb0 {
@@ -170,6 +179,11 @@ hscif0_pins: hscif0 {
 		function = "hscif0";
 	};
 
+	hscif2_pins: hscif2 {
+		groups = "hscif2_data", "hscif2_ctrl";
+		function = "hscif2";
+	};
+
 	i2c0_pins: i2c0 {
 		groups = "i2c0";
 		function = "i2c0";
@@ -190,6 +204,11 @@ scif_clk_pins: scif-clk {
 		groups = "scif_clk";
 		function = "scif_clk";
 	};
+
+	scif_clk2_pins: scif-clk2 {
+		groups = "scif_clk2";
+		function = "scif_clk2";
+	};
 };
 
 &rpc {
@@ -228,3 +247,7 @@ &rwdt {
 &scif_clk {
 	clock-frequency = <24000000>;
 };
+
+&scif_clk2 {
+	clock-frequency = <24000000>;
+};