feat(boards): Add Mikoto board

* Supports selecting from several possible charge currents

Co-authored-by: Pete Johanson <peter@peterjohanson.com>

app/boards/arm/mikoto/mikoto_520.dts

@@ -0,0 +1,115 @@
+/*
+ * Copyright (c) 2020 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+/dts-v1/;
+#include <nordic/nrf52840_qiaa.dtsi>
+#include "arduino_pro_micro_pins.dtsi"
+
+/ {
+	model = "mikoto";
+	compatible = "zhiayang,mikoto";
+
+	chosen {
+		zephyr,code-partition = &code_partition;
+		zephyr,sram = &sram0;
+		zephyr,flash = &flash0;
+	};
+
+	leds {
+		compatible = "gpio-leds";
+		blue_led: led_0 {
+			gpios = <&gpio0 15 GPIO_ACTIVE_HIGH>;
+			label = "Blue LED";
+		};
+	};
+
+	ext-power {
+		compatible = "zmk,ext-power-generic";
+		label = "EXT_POWER";
+		control-gpios = <&gpio0 13 GPIO_ACTIVE_LOW>;
+	};
+
+	vbatt {
+		compatible = "zmk,battery-voltage-divider";
+		label = "BATTERY";
+		io-channels = <&adc 2>;
+		output-ohms = <10000000>;
+		full-ohms = <(10000000 + 4000000)>;
+	};
+};
+
+&adc {
+	status = "okay";
+};
+
+&gpiote {
+	status = "okay";
+};
+
+&gpio0 {
+	status = "okay";
+};
+
+&gpio1 {
+	status = "okay";
+};
+
+&i2c0 {
+	compatible = "nordic,nrf-twi";
+	sda-pin = <17>;
+	scl-pin = <20>;
+};
+
+&uart0 {
+	compatible = "nordic,nrf-uarte";
+	tx-pin = <8>;
+	rx-pin = <4>;
+};
+
+&usbd {
+	status = "okay";
+};
+
+
+&flash0 {
+	/*
+	 * For more information, see:
+	 * http://docs.zephyrproject.org/latest/devices/dts/flash_partitions.html
+	 */
+	partitions {
+		compatible = "fixed-partitions";
+		#address-cells = <1>;
+		#size-cells = <1>;
+
+		sd_partition: partition@0 {
+			label = "softdevice";
+			reg = <0x00000000 0x00026000>;
+		};
+		code_partition: partition@26000 {
+			label = "code_partition";
+			reg = <0x00026000 0x000c6000>;
+		};
+
+		/*
+		 * The flash starting at 0x000ec000 and ending at
+		 * 0x000f3fff is reserved for use by the application.
+		 */
+
+		/*
+		 * Storage partition will be used by FCB/LittleFS/NVS
+		 * if enabled.
+		 */
+		storage_partition: partition@ec000 {
+			label = "storage";
+			reg = <0x000ec000 0x00008000>;
+		};
+
+		boot_partition: partition@f4000 {
+			label = "adafruit_boot";
+			reg = <0x000f4000 0x0000c000>;
+		};
+	};
+};