ramips: add support for HiWiFi HC5611

ramips: add support for HiWiFi HC5611

CPU: MediaTek MT7628AN @ 575 MHz
Flash: 16 MB
RAM: 128 MB
Ethernet: 10/100Mbps x 1
Wlan: 300 Mbps
USB: USB 2.0 x 1
LED: red/green x 1
Button: reset x 1

1. Open https://www.hiwifi.wtf/, Get Cloud token and unlock ssh
2. Upload the openwrt firmware to the router via SCP
3. Login the router via SSH
4. Run `mtd -r write path_to_firmware.bin firmware`

I have tested on my device.
- The LED will display RED on power-on, After system start completed, trun GREEN
- Reset button working now. Long press after 5s will reset factory. Short press less 1s will reboot the device
- USB can working under official u-boot

Signed-off-by: Senis John <thank243@gmail.com>