ramips: add support for VoCore2

This patch adds support for the VoCore VoCore2 and its complementary
"ultimate" dock.

Specifications:
- SoC: MediaTek MT7628AN (580MHz, ramips)
- RAM: 128MB DDR2 166MHz
- Storage: 16MB NOR SPI flash onboard + microSD slot on dock
- Wireless: Built into MT7628AN (mt76) with 1T1R firmware on VoCore2
            boards with onboard 1x chip antenna
- Ethernet: 1x100M (port0) on dock, 1x100M (port2) on PCB header
- Dock hardware:
  - USB 2.0 socket
  - MicroSD socket
  - 100Mbps Ethernet x1
  - 3.5mm headphone jack (TRRS) connected to Everest Semi ES8388 I2S
    DAC/ADC (support WIP)
  - Micro USB for power and console (UART2)

Initial installation:
- VoCore2 comes preinstalled with a fork of OpenWrt CC and AP on
  SSID "VoCore2"
- Connect to VoCore2 by Ethernet or Wi-Fi
- `ssh root@192.168.1.1` (password is "vocore")
- scp/wget/etc. LEDE sysupgrade.bin to VoCore2
- `sysupgrade -n <your image>.bin` (don't keep old config, as the
  original firmware uses Ralink SDK Wi-Fi drivers and not
  mt76+mac80211)
- after sysupgrade completes, Wi-Fi will be disabled by default so use
  Ethernet or the micro USB console to configure Wi-Fi again

Signed-off-by: Andrew Yong <me@ndoo.sg>

target/linux/ramips/dts/VOCORE2.dts

@@ -0,0 +1,123 @@
+/dts-v1/;
+
+#include "mt7628an.dtsi"
+
+#include <dt-bindings/gpio/gpio.h>
+#include <dt-bindings/input/input.h>
+
+/ {
+	compatible = "vocore,VoCore2", "mediatek,mt7628an-soc";
+	model = "VoCore2";
+
+	chosen {
+		bootargs = "console=ttyS2,115200";
+	};
+
+	memory@0 {
+		device_type = "memory";
+		reg = <0x0 0x4000000>;
+	};
+
+	gpio-leds {
+		compatible = "gpio-leds";
+
+		status {
+			label = "vocore2:fuchsia:status";
+			gpios = <&gpio1 12 GPIO_ACTIVE_LOW>;
+		};
+	};
+};
+
+&pinctrl {
+	state_default: pinctrl0 {
+		gpio {
+			ralink,group = "refclk", "gpio";
+			ralink,function = "gpio";
+		};
+
+		agpio {
+			ralink,group = "agpio";
+			ralink,function = "uart2";
+		};
+	};
+
+	uart1_pins: uart1 {
+		uart1 {
+			ralink,group = "uart1";
+			ralink,function = "uart1";
+		};
+	};
+
+	uart2_pins: uart2 {
+		uart2 {
+			ralink,group = "spis";
+			ralink,function = "pwm";
+		};
+	};
+};
+
+&wmac {
+	status = "okay";
+	ralink,mtd-eeprom = <&factory 0x4>;
+};
+
+&spi0 {
+	status = "okay";
+
+	m25p80@0 {
+		#address-cells = <1>;
+		#size-cells = <1>;
+		compatible = "jedec,spi-nor";
+		reg = <0>;
+		spi-max-frequency = <10000000>;
+		m25p,chunked-io = <32>;
+
+		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;
+		};
+
+		partition@50000 {
+			label = "firmware";
+			reg = <0x50000 0xfb0000>;
+		};
+	};
+};
+
+&esw {
+	mediatek,portmap = <0x7>;
+	mediatek,portdisable = <0x3a>;
+};
+
+&i2s {
+	status = "okay";
+};
+
+&gdma {
+	status = "okay";
+};
+
+&pwm {
+	status = "okay";
+};
+
+&uart1 {
+	status = "okay";
+};
+
+&uart2 {
+	status = "okay";
+};