ramips: add support for JS76x8 series DEV boards

ramips: add support for JS76x8 series DEV boards

This commit adds support for the Jotale JS76x8 series development boards.
These devices have the following specifications:

- SOC: MT7628AN/NN, MT7688AN, MT7628DAN
- RAM of MT7628AN/NN and MT7688AN: 64/128/256 MB (DDR2)
- RAM of MT7628DAN: 64 MB (DDR2)
- FLASH:8/16/32 MB (SPI NOR)
- Ethernet:3x 10/100 Mbps ethernet ports (MT76x8 built-in switch)
- WIFI:1x 2T2R 2.4 GHz Wi-Fi
- LEDs:1x system status green LED, 1x wifi green LED,
       3x ethernet green LED
- Buttons:1x reset button
- 1x microSD slot
- 4x USB 2.0 port
- 1x mini-usb debug UART
- 1x DC jack for main power (DC 5V)
- 1x TTL/RS232 UART
- 1x TTL/RS485 UART
- 13x GPIO header
- 1x audio codec(wm8960)

Installation via OpenWrt:

The original firmware is OpenWrt, so both LuCI and sysupgrade can be used.

Installation via U-boot web:

1. Power on board with reset button pressed, release it
   after wifi led start blinking.
2. Setup static IP 192.168.1.123/4 on your PC.
3. Go to 192.168.1.8 in browser and upload "sysupgrade" image.

Installation via U-boot tftp:
1. Connect to serial console at the mini usb, which has been connected to UART0
   on board (115200 8N1)
2. Setup static IP 192.168.1.123/4 on your PC.
3. Place openwrt-firmware.bin on your PC tftp server (192.168.1.123).
3. Connect one of LAN ports on board to your PC.
4. Start terminal software (e.g. screen /dev/ttyUSB0 115200) on PC.
5. Apply power to board.
6. Interrupt U-boot with keypress of "2".
7. At u-boot prompts:
   Warning!! Erase Linux in Flash then burn new one. Are you sure?(Y/N) Y
   Input device IP (192.168.1.8) ==:192.168.1.8
   Input server IP (192.168.1.123) ==:192.168.1.123
   Input Linux Kernel filename (root_uImage) ==:openwrt-firmware.bin
8. board will download file from tftp server, write it to flash and reboot.

Signed-off-by: Robinson Wu <wurobinson@qq.com>
[add license to DTS files, fix state_default and reduce to the mimimum,
move phy0tpt trigger to DTS, drop ucidef_set_led_timer, fix network ports]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>