ath79: add support for ASUS PL-AC56

ath79: add support for ASUS PL-AC56

Asus PL-AC56 Powerline Range Extender Rev.A1
(in kit with Asus PL-E56P Powerline-slave)

Hardware specifications:
Board: AP152
SoC: QCA9563 2.4G n 3x3
PLC: QCA7500
WiFi: QCA9882 5G ac 2x2
Switch: QCA8337 3x1000M
Flash: 16MB 25L12835F SPI-NOR
DRAM SoC: 64MB w9751g6kb-25
DRAM PLC: 128MB w631gg6kb-15

Clocks: CPU:775.000MHz, DDR:650.000MHz, AHB:258.333MHz, Ref:25.000MHz

MAC addresses as verified by OEM firmware:
use address source
Lan/Wan/PLC *:10 art 0x1002 (label)
2G *:10 art 0x1000
5G *:14 art 0x5000

Important notes:

the PLC firmware has to be provided and copied manually onto the
device! The PLC here has no dedicated flash, thus the firmware file
has to be uploaded to the PLC controller at every system start
the PLC functionality is managed by the script /etc/init.d/plc_basic,
a very basic script based on the the one from Netadair (netadair dot de)
Installation:

Asus windows recovery tool:

have to have the latest Asus firmware flashed before continuing!
install the Asus firmware restoration utility
unplug the router, hold the reset button while powering it on
release when the power LED flashes slowly
specify a static IP on your computer:
IP address: 192.168.1.75
Subnet mask 255.255.255.0
start the Asus firmware restoration utility, specify the factory image
and press upload
do NOT power off the device after OpenWrt has booted until the LED flashing
TFTP Recovery method:

have to have the latest Asus firmware flashed before continuing!
set computer to a static ip, 192.168.1.75
connect computer to the LAN 1 port of the router
hold the reset button while powering on the router for a few seconds
send firmware image using a tftp client; i.e from linux:
$ tftp
tftp> binary
tftp> connect 192.168.1.1
tftp> put factory.bin
tftp> quit
do NOT power off the device after OpenWrt has booted until the LED flashing
Additional notes:

the pairing buttons have to have pressed for at least half a second,
it doesn't matter on which plc device (master or slave) first
it is possible to pair the devices without the button-pairing requirement
simply by pressing reset on the slave device. This will default to the
firmware settings, which is also how the plc_basic script is setting up
the master device, i.e. configuring it to firmware defaults
the PL-E56P slave PLC has its dedicated 4MByte SPI, thus it is capable
to store all firmware currently available. Note that some other
slave devices are not guarantied to have the capacity for the newer
~1MByte firmware blobs!
To have a good overlook about the slave device, here are its specs:
same QCA7500 PLC controller, same w631gg6kb-15 128MB RAM,
25L3233F 4MB SPI-NOR and an AR8035-A 1000M-Transceiver

Signed-off-by: Tamas Balogh <tamasbalogh@hotmail.com>