Netgear Nighthawk RAX120v2 AX WIFI router with 5 1G and 1 5G ports.

The majority of the code is based on @jewwest's PR #11830.

Specifications:
    * CPU: Qualcomm IPQ8074 Quad core Cortex-A53 2.2GHz
    * RAM: 1024MB of DDR3 (Nanya NT5CC256M16EP-EK × 2)
    * Flash: SPI-NAND 512 MiB (Winbond W29N04GZBIBA)
    * Ethernet: 4x 10/100/1000 Mbps LAN,
                1x 10/100/1000 Mbps WAN (Qualcomm QCA8075),
                1x 10/100/1000/2500/5000 Mbps LAN/WAN (Aquantia AQR111B0 PHY)
    * Wi-Fi:
        * 2.4 GHz: Qualcomm QCN5024 4x4
        * 2x 5 GHz: Qualcomm QCN5054 4x4
    * USB: 2x USB 3.0
    * LEDs: Power, 2.4GHz & 5GHz Radio, WPS, WAN, USB1 & USB2, 5G LAN
    * Keys: LEDs On/Off, Power, Reset, RFKILL, WPS
    * UART: Marked J9003 VCC TX RX GND, beginning from "1". 3.3v, 115200n8
    * Power: 19 VDC, 3.1 A

Installation:
    * Flashing OpenWrt is done in two steps:
        a) Flash *-squashfs-web-ui-factory.img from stock UI (thanks to @wangyu-).
           This writes an initramfs based OpenWrt image onto the RAX120v2
        b) From OpenWrt flash the *-squashfs-sysupgrade.bin using LuCI or the commandline

    * U-Boot allows booting an initramfs image via TFTP:
    - Set ip of your PC to 192.168.1.100
        - At the serial console interrupt boot at "Hit any key to stop autoboot:"
        - In u-boot run `tftpsrv`
        - On your PC send the OpenWrt initramfs image:

          tftp 192.168.1.1 -m binary -c put openwrt-ipq807x-generic-netgear_rax120v2-initramfs-uImage.itb

Make 5G Aquantia phy work:
    For the 5G port labeled 'lan5' to work a firmware is needed. This can be loaded in
    u-boot by writing the firmware to the correct mtd partition.

    The firmware file found in the Netgear stock firmware under /lib/firmware/ named
    'AQR-G3_v4.3.C-AQR_DNI_DR-EQ35AX8-R-prov1_ID23888_VER1311.cld' is needed and has to
    be converted to a MBN file.

    The `mkheader.py` script used here can be found in the Netgear V1.2.8.40 GPL source,
    under 'git_home/u-boot.git/tools/mkheader.py'

    Convert the CLD file to MBN using:
    $ python2 mkheader.py 0x44000000 0x13 <*.cld file> aqr_4.3.C.mbn

    This MBN file can then be flashed to the MTD partition to be used by u-boot.

    The necessary files can also be found in
        https://github.com/boretom/openwrt-fork/tree/rax120v2/aquantia-firmware

    * Write MBN file to MTD partition to be loaded automatically by u-boot:

      U-boot automatically tries to load the firmware from nand at address 0x7e00000 which
      corresponds to `/dev/mtd25` in OpenWrt.

        - find ETHPHYFW partition while running OpenWrt (expected: /dev/mtd25)

          $ fgrep -i 'ethphyfw' /proc/mtd
          mtd25: 00080000 00020000 "ethphyfw

        - copy mbn file to /tmp/ folder of the router

          $ scp aqr-v4.3.C.mbn 192.168.1.1:/tmp/

        - write mbn file to ethphyfw partition

          $ mtd write /tmp/aqr_v4.3.C.mbn /dev/mtd25

Revert to stock firmware:
    * Flash the stock firmware to the bootloader using TFTP/NMRP.

References to RAX120v2 GPL source:
    https://www.downloads.netgear.com/files/GPL/RAX120-V1.2.8.40_gpl_src.zipReviewed-by: NRobert Marko <robimarko@gmail.com>
Signed-off-by: NThomas Kupper <thomas.kupper@gmail.com>