ramips: add support for D-Link DAP-1620 B1

The DAP-1620 rev B is a wall-plug AC1300 repeater.

Specifications:
- MT7621AT, 256 MiB RAM, 16 MiB SPI NOR
- MT7615DN 2x2 802.11n +2x2 802.11ac (DBDC)
- Ethernet: 1 port 10/100/1000
- Status LEDs (1x red+green)
- LED RSSI bargraph (2x green, 1x red+green)

Installation:
- Keep reset button pressed during plug-in
- Web Recovery Updater is at 192.168.0.50
- Upload factory.bin, confirm flashing
  (seems to work best with Chromium-based browsers)

Revert to OEM firmware:
- tail -c+117 DAP1620B1_FW212B03.bin | \
  openssl aes-256-cbc -d -md md5 -out decrypted.bin \
  -k 905503a4e0c3cd3c1ce062246de427a68962347e
- flash decrypted.bin via D-Link Web Recovery

Signed-off-by: Rani Hod <rani.hod@gmail.com>

target/linux/ramips/dts/mt7621_dlink_dap-1620-b1.dts

@@ -0,0 +1,158 @@
+// SPDX-License-Identifier: GPL-2.0-or-later OR MIT
+
+#include "mt7621.dtsi"
+
+#include <dt-bindings/gpio/gpio.h>
+#include <dt-bindings/input/input.h>
+
+/ {
+	compatible = "dlink,dap-1620-b1", "mediatek,mt7621-soc";
+	model = "D-Link DAP-1620 B1";
+
+	aliases {
+		label-mac-device = &gmac0;
+
+		led-boot = &led_status_red;
+		led-failsafe = &led_status_green;
+		led-running = &led_status_green;
+		led-upgrade = &led_status_red;
+	};
+
+	keys {
+		compatible = "gpio-keys";
+
+		reset {
+			label = "reset";
+			gpios = <&gpio 7 GPIO_ACTIVE_LOW>;
+			linux,code = <KEY_RESTART>;
+			debounce-interval = <60>;
+		};
+
+		wps {
+			label = "wps";
+			gpios = <&gpio 18 GPIO_ACTIVE_LOW>;
+			linux,code = <KEY_WPS_BUTTON>;
+		};
+	};
+
+	leds {
+		compatible = "gpio-leds";
+
+		led_status_red: status_red {
+			label = "red:status";
+			gpios = <&gpio 16 GPIO_ACTIVE_LOW>;
+		};
+
+		led_status_green: status_green {
+			label = "green:status";
+			gpios = <&gpio 13 GPIO_ACTIVE_LOW>;
+		};
+
+		rssi_low_red {
+			label = "red:rssilow";
+			gpios = <&gpio 25 GPIO_ACTIVE_LOW>;
+		};
+
+		rssi_low_green {
+			label = "green:rssilow";
+			gpios = <&gpio 24 GPIO_ACTIVE_LOW>;
+		};
+
+		rssi_med_green {
+			label = "green:rssimed";
+			gpios = <&gpio 23 GPIO_ACTIVE_LOW>;
+		};
+
+		rssi_high_green {
+			label = "green:rssihigh";
+			gpios = <&gpio 22 GPIO_ACTIVE_LOW>;
+		};
+	};
+};
+
+&spi0 {
+	status = "okay";
+
+	flash@0 {
+		compatible = "jedec,spi-nor";
+		reg = <0>;
+		spi-max-frequency = <50000000>;
+
+		partitions {
+			compatible = "fixed-partitions";
+			#address-cells = <1>;
+			#size-cells = <1>;
+
+			partition@0 {
+				label = "u-boot";
+				reg = <0x0 0x30000>;
+				read-only;
+			};
+
+			partition@30000 {
+				label = "u-boot-env";
+				reg = <0x30000 0x10000>;
+				read-only;
+			};
+
+			factory: partition@40000 {
+				label = "factory";
+				reg = <0x40000 0x10000>;
+				read-only;
+
+				compatible = "nvmem-cells";
+				#address-cells = <1>;
+				#size-cells = <1>;
+
+				macaddr_factory_e000: macaddr@e000 {
+					reg = <0xe000 0x6>;
+				};
+			};
+
+			partition@50000 {
+				compatible = "denx,uimage";
+				label = "firmware";
+				reg = <0x50000 0xfb0000>;
+			};
+		};
+	};
+};
+
+&pcie {
+	status = "okay";
+};
+
+&pcie0 {
+	wifi@0,0 {
+		compatible = "mediatek,mt76";
+		reg = <0x0000 0 0 0 0>;
+		mediatek,mtd-eeprom = <&factory 0x0>;
+		/* The correct MAC addresses are set in 10_fix_wifi_mac. */
+	};
+};
+
+&gmac0 {
+	nvmem-cells = <&macaddr_factory_e000>;
+	nvmem-cell-names = "mac-address";
+};
+
+&switch0 {
+	ports {
+		port@0 {
+			status = "okay";
+			label = "lan";
+		};
+	};
+};
+
+&ethernet {
+	pinctrl-0 = <&mdio_pins>, <&rgmii1_pins>;
+};
+
+&state_default {
+	gpio {
+		groups = "uart3", "jtag", "wdt";
+		function = "gpio";
+	};
+};
+