econet: New device: Zyxel PMG5617GA

econet: New device: Zyxel PMG5617GA

This device has one USB2.0 port, plus ethernet, 2x wifi, ethernet, xPON
and VoIP.

Installation instructions: (Assuming root shell via SSH or serial)
1. Place OpenWrt TRX file on a USB stick formatted VFAT
2. Plug in the stick to the modem
3. Type: mtd write -f -e tclinux /mnt/usb2_sda1/<name of file>.trx tclinux

At this point, both OpenWrt and the vendor OS will be installed
because the device has space for two operating systems. Switch the OS
to boot to OpenWrt:

1. mtd readflash tmpdata 999999999 0 reservearea
2. echo -n '0' | dd of=./tmpdata bs=1 count=1 seek=397311 conv=notrunc
3. mtd write -f -e reservearea ./tmpdata reservearea
4. reboot

WARNING: While you can install with SSH alone, you need serial to use
OpenWrt on EcoNet devices because the Ethernet driver has not yet been
developed.

Signed-off-by: Caleb James DeLisle <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/20580
Signed-off-by: Hauke Mehrtens <[email protected]>