ramips: Xiaomi MIR3G: detect board name from DTS

ramips: Xiaomi MIR3G: detect board name from DTS

- Former "mir3g" board name becomes "xiaomi,mir3g".
- Reorder some entries to maintain alphabetical order.
- Change DTS so status LEDs (yellow/red/blue) mimic
  Xiaomi stock firmware: (Section Indicator)
<http://files.xiaomi-mi.co.uk/files/router_pro/router%20PRO%20EN.pdf>
<http://files.xiaomi-mi.co.uk/files/Mi_WiFi_router_3/MiWiFi_router3_EN.pdf>
|Yellow: Update (LED flickering), the launch of the system (steady light);
|Blue: during normal operation (steady light);
|Red: Safe mode (display flicker), system failure (steady light);

Signed-off-by: Ozgur Can Leonard <ozgurcan@gmail.com>
[Added link to similar Router 3 model]
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>