ipq40xx: add support for Teltonika RUTX50

ipq40xx: add support for Teltonika RUTX50

Hardware
--------
CPU:     Qualcomm IPQ4018
RAM:     256M
Flash:   16MB SPI-NOR (W25Q128)
         128MB SPI-NAND (XTX)
WiFi:    2T2R (2GHz 802.11n ; 5 GHz 802.11ac)
ETH:     4x LAN ; 1x WAN (Gigabit)
CELL:    Quectel RG501Q 3G/4G/5G

UART: Available on the goldfinger connector (Pinout silkscreened)
      115200 8N1 3V3 - Only connect RX / TX / GND

Installation
------------

1. Enable SSH in the Teltonika UI
   (System --> Administration --> Access Control)

2. Check from which partition set the device is currently running from.

   $ cat /proc/boot_info/rootfs/primaryboot

   In case this output reads 0, install a Software update from Teltonika
   first. After upgrade completion, check this file now reads 1 before
   continuing.

2. Transfer the OpenWrt factory image to the device using scp. Use the
   same password (user root!) as used for the Web-UI.

   $ scp -O openwrt-factory.bin root@192.168.1.1:/tmp

3. Connect to the device using ssh as the root user.

4. Install OpenWrt by writing the factory image to flash.

   $ ubiformat /dev/mtd16 -y -f /tmp/openwrt-factory.bin

5. Instruct the bootloaer to boot from the first partition set.

   $ echo 0 > /proc/boot_info/rootfs/primaryboot
   $ cat /proc/boot_info/getbinary_bootconfig > /tmp/bootconfig.bin
   $ cat /proc/boot_info/getbinary_bootconfig1 > /tmp/bootconfig1.bin
   $ mtd write /tmp/bootconfig.bin /dev/mtd2
   $ mtd write /tmp/bootconfig1.bin /dev/mtd3

6. Reboot the device.

   $ reboot

Signed-off-by: David Bauer <mail@david-bauer.net>
(cherry picked from commit 844bb4bfad84cc6267f9b138d1f63b07ed3b77d0)