MIPS: ath79: add initial support for TP-LINK MR3020

The following features are supported:

* UART;
* SPI-flash;
* USB host;
* GPIO keys and LEDs.

Links:

* http://www.tp-link.com/en/products/details/?model=TL-MR3020
* http://wiki.openwrt.org/toh/tp-link/tl-mr3020
* https://wikidevi.com/wiki/TP-LINK_TL-MR3020

Signed-off-by: Antony Pavlov <[e-mail]>
Cc: Gabor Juhos <[e-mail]>
Cc: Alban Bedel <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Patchwork: https://patchwork.linux-mips.org/patch/12880/
Signed-off-by: Ralf Baechle <[e-mail]>

arch/mips/boot/dts/qca/Makefile

···
 # All DTBs
 dtb-$(CONFIG_ATH79)			+= ar9132_tl_wr1043nd_v1.dtb
+dtb-$(CONFIG_ATH79)			+= ar9331_tl_mr3020.dtb
 
 # Force kbuild to make empty built-in.o if necessary
 obj-				+= dummy.o

arch/mips/boot/dts/qca/ar9331_tl_mr3020.dts

···
+/dts-v1/;
+
+#include <dt-bindings/gpio/gpio.h>
+#include <dt-bindings/input/input.h>
+
+#include "ar9331.dtsi"
+
+/ {
+	model = "TP-Link TL-MR3020";
+	compatible = "tplink,tl-mr3020";
+
+	aliases {
+		serial0 = &uart;
+	};
+
+	memory@0 {
+		device_type = "memory";
+		reg = <0x0 0x2000000>;
+	};
+
+	leds {
+		compatible = "gpio-leds";
+
+		wlan {
+			label = "tp-link:green:wlan";
+			gpios = <&gpio 0 GPIO_ACTIVE_HIGH>;
+			default-state = "off";
+		};
+
+		lan {
+			label = "tp-link:green:lan";
+			gpios = <&gpio 17 GPIO_ACTIVE_LOW>;
+			default-state = "off";
+		};
+
+		wps {
+			label = "tp-link:green:wps";
+			gpios = <&gpio 26 GPIO_ACTIVE_LOW>;
+			default-state = "off";
+		};
+
+		led3g {
+			label = "tp-link:green:3g";
+			gpios = <&gpio 27 GPIO_ACTIVE_LOW>;
+			default-state = "off";
+		};
+	};
+
+	gpio-keys-polled {
+		compatible = "gpio-keys-polled";
+		#address-cells = <1>;
+		#size-cells = <0>;
+		poll-interval = <100>;
+
+		button@0 {
+			label = "wps";
+			linux,code = <KEY_WPS_BUTTON>;
+			gpios = <&gpio 11 GPIO_ACTIVE_HIGH>;
+		};
+
+		button@1 {
+			label = "sw1";
+			linux,code = <BTN_0>;
+			gpios = <&gpio 18 GPIO_ACTIVE_HIGH>;
+		};
+
+		button@2 {
+			label = "sw2";
+			linux,code = <BTN_1>;
+			gpios = <&gpio 20 GPIO_ACTIVE_HIGH>;
+		};
+	};
+
+	reg_usb_vbus: reg_usb_vbus {
+		compatible = "regulator-fixed";
+		regulator-name = "usb_vbus";
+		regulator-min-microvolt = <5000000>;
+		regulator-max-microvolt = <5000000>;
+		gpio = <&gpio 8 GPIO_ACTIVE_HIGH>;
+		enable-active-high;
+	};
+};
+
+&ref {
+	clock-frequency = <25000000>;
+};
+
+&uart {
+	status = "okay";
+};
+
+&gpio {
+	status = "okay";
+};
+
+&usb {
+	dr_mode = "host";
+	vbus-supply = <&reg_usb_vbus>;
+	status = "okay";
+};
+
+&usb_phy {
+	status = "okay";
+};
+
+&spi {
+	num-chipselects = <1>;
+	status = "okay";
+
+	/* Spansion S25FL032PIF SPI flash */
+	spiflash: s25sl032p@0 {
+		#address-cells = <1>;
+		#size-cells = <1>;
+		compatible = "spansion,s25sl032p", "jedec,spi-nor";
+		spi-max-frequency = <104000000>;
+		reg = <0>;
+	};
+};