ipq40xx: add support for devolo Magic 2 WiFi next

ipq40xx: add support for devolo Magic 2 WiFi next

SOC:     IPQ4018 / QCA Dakota
CPU:     Quad-Core ARMv7 Processor rev 5 (v71) Cortex-A7
DRAM:    256 MiB
NOR:     32 MiB
ETH:     Qualcomm Atheros QCA8075 (2 ports)
PLC:     MaxLinear G.hn 88LX5152
WLAN1:   Qualcomm Atheros QCA4018 2.4GHz 802.11bgn 2:2x2
WLAN2:   Qualcomm Atheros QCA4018 5GHz 802.11a/n/ac 2:2x2
INPUT:   RESET, WiFi, PLC Button
LEDS:    red/white home, white WiFi

To modify a retail device to run OpenWRT firmware:
1) Setup a TFTP server on IP address 192.168.0.100 and copy the OpenWRT
   initramfs (initramfs-fit-uImage.itb) to the TFTP root as 'uploadfile'.
2) Power on the device while pressing the recessed reset button next to
   the Ethernet ports. This causes the bootloader to retrieve and start
   the initramfs.
3) Once the initramfs is booted, the device will come up with IP
   192.168.1.1. You can then connect through SSH (allow some time for
   the first connection).
4) On the device shell, run 'fw_printenv' to show the U-boot environment.
   Backup this information since it contains device unique factory data.
5) Change the boot command to support booting OpenWRT:
   # fw_setenv bootcmd 'sf probe && sf read 0x84000000 0x180000 0x400000 && bootm'
6) Change directory to /tmp, download the sysupgrade (e.g. through wget)
   and install it with sysupgrade. The device will reboot into OpenWRT.

Notice that there is currently no support for booting the G.hn chip.
This requires userland software we lack the rights to share right now.

Signed-off-by: Stefan Schake <stefan.schake@devolo.de>