ARM: dts: mmp3-dell-ariel: Add the power button node

This adds support for the power button attached to the Embedded Controller
on a Dell Wyse 3020 "Ariel" board.

However, while the EC itself is controlled via I2C, the input capability
for the power button acts as a separate device attached to the SPI, hence
it has a separate device node.
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Link: https://lore.kernel.org/r/20210121034130.1381872-11-lkundrak@v3.sk'
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm/boot/dts/mmp3-dell-ariel.dts

@@ -119,8 +119,16 @@ firmware-flash@0 {
 };
 
 &ssp2 {
-	cs-gpios = <&gpio 56 GPIO_ACTIVE_LOW>;
 	status = "okay";
+	cs-gpios = <&gpio 56 GPIO_ACTIVE_LOW>;
+
+	power-button@0 {
+		reg = <0>;
+		interrupt-parent = <&gpio>;
+		interrupts = <60 IRQ_TYPE_EDGE_RISING>;
+		compatible = "dell,wyse-ariel-ec-input", "ene,kb3930-input";
+		spi-max-frequency = <33000000>;
+	};
 };
 
 &gpu_2d {