ARM: shmobile: genmai reference dts: Add RSPI node

Add SPI device for RSPI on Genmai.

On this board, only rspi4 is in use. Its bus contains a single device
(a wm8978 audio codec), for which no bindings are defined yet.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm/boot/dts/r7s72100-genmai.dts

@@ -57,3 +57,13 @@ eeprom@50 {
 &scif2 {
 	status = "okay";
 };
+
+&spi4 {
+	status = "okay";
+
+	codec: codec@0 {
+		compatible = "wlf,wm8978";
+		reg = <0>;
+		spi-max-frequency = <5000000>;
+	};
+};