ramips: mt76x8: add support for MERCUSYS MB130-4G v1

ramips: mt76x8: add support for MERCUSYS MB130-4G v1

Specification:
SoC: MediaTek MT7628AN
RAM: 128 MB, Zentel A3R1GE40JBF-8E
Flash: 16MB, Winbond W25Q128JV
Switch: rt3050-esw, 2 ports 100 Mbps
WiFi: MediaTek mt7628-wmac 2.4GHz 802.11n and MediaTek MT7663 5GHz
  802.11ac (PCIe)
WWAN: Quectel EC200A-EL 4G modem (USB)
GPIO:
  * 1 button (Reset/WPS)
  * 6 LEDs (Power+WPS, LAN, 3xSignal)
  * USB port power controls
  * Modem reset
  * Modem programming switch
  * Internal/external antenna switch for 4G

Serial Interface:
  TP10 - 3.3V can be used for level shifter, if needed
  TP9 - TX
  TP8 - RX
  TP11 - GND
Interface properties: 115200, 8N1

Access to console using serial port for OEM firmware:
Username: admin
Password: 1234

Flashing via TFTP (no disassembling or soldering required):
1. Connect your PC and router to port LAN
2. Configure PC interface using static IP 192.168.1.225, mask
   255.255.255.0
3. Place OpenWRT firmware image (*-squashfs-tftp-recovery.bin) to TFTP
   root folder and renamed it to tp_recovery.bin
4. Unplug power from router
5. Press and hold Reset/WPS button
6. Power up the router
7. Wait until TFTP started uploading image (~10 seconds after power up)
   and release Reset/WPS button
8. Wait until image uploaded, i.e. until LAN LED start lighting
9. Enable DHCP address on PC interface and wait for assigning address
10. Use ssh (root@192.168.1.1) to configure router properties

Depends on patch for firmware-utils package:
https://github.com/openwrt/firmware-utils/commit/2051fe5b

Signed-off-by: Sergii Shcherbakov <shchers@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/17819
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>