ramips: further improve support for Xiaomi MiWiFi Nano

ramips: further improve support for Xiaomi MiWiFi Nano

This patch does the following:

- prepend vendor name to model
- set status LEDs to follow the behavior in stock FW
- simplify state_default node definition
- use generic name for flash node

Stock FW status indicators:
https://files.xiaomi-mi.com/files/Mi_Router_Wi-Fi_Nano/Mi_router-NANO_EN.pdf
> Yellow: power on / off
> Blue: during normal operation
> Red: in case of problems with the operation of the device

Signed-off-by: Sungbo Eo <mans0n@gorani.run>