ramips: add support for Kroks Rt-Cse SIM Injector DS

ramips: add support for Kroks Rt-Cse SIM Injector DS

Aka Kroks Rt-Cse5 UW DRSIM (KNdRt31R16), ID 1958:
https://kroks.ru/search/?text=1958
See Kroks OpenWrt fork for support of other models:
https://github.com/kroks-free/openwrt

Device specs:
- CPU: MediaTek MT7628AN
- Flash: 16MB SPI NOR
- RAM: 64MB
- Bootloader: U-Boot
- Ethernet: 5x 10/100 Mbps
- 2.4 GHz: b/g/n SoC
- USB: 1x
- SIM-reader: 2x (driven by a dedicated chip with it's own firmware)
- Buttons: reset
- LEDs: 1x Power, 1x Wi-Fi, 12x others (SIM status, Internet, etc.)

Flashing:
- sysupgrade image via stock firmware WEB interface, IP: 192.168.1.254
- U-Boot launches a WEB server if Reset button is held during power up,
  IP: 192.168.1.1

MAC addresses as verified by OEM firmware:
vendor   OpenWrt   source
LAN      eth0      factory 0x4 (label)
2g       wlan0     label

Signed-off-by: Andrey Butirsky <butirsky@gmail.com>