ath79: add support for ZTE MF282

ath79: add support for ZTE MF282

The ZTE MF282 is a LTE router used (exclusively?) by the network operator
"3".

Specifications
==============

SoC: QCA9563 (775MHz)
RAM: 128MiB
Flash: 8MiB SPI-NOR + 128MiB SPI-NAND
LAN: 1x GBit LAN
LTE: ZTE MF270 (Cat4), detected as P685M
WiFi: QCA9880ac + QCA9560bgn

MAC addresses
=============

LAN: from config
WiFi 1: from config
WiFi 2: +1

Installation
============

TFTP installation using UART is preferred. Disassemble the device and
connect serial. Put the initramfs image as openwrt.bin to your TFTP server
and configure a static IP of 192.168.1.100. Load the initramfs image by
typing:

  setenv serverip 192.168.1.100
  setenv ipaddr 192.168.1.1
  tftpboot 0x82000000 openwrt.bin
  bootm 0x82000000

From this intiramfs boot you can take a backup of the currently installed
partitions as no vendor firmware is available for download.

Once booted, transfer the sysupgrade image and run sysupgrade.

LTE Modem
=========

The LTE modem is probably the same as in the MF283+, all instructions
apply.

Configuring the connection using modemmanager works properly, the modem
provides three serial ports and a QMI CDC ethernet interface.

Signed-off-by: Andreas Böhler <dev@aboehler.at>