ipq807x: add support for Yuncore AX880

ipq807x: add support for Yuncore AX880

SPECIFICATION:
    - Chipset:  IPQ8072A +QCN5054+QCN5024+QCA8081*2
    - Flash NOR-8MB AND NAND-128MB
    - RAM 1Gb DDR
    - IEEE 802.11:  802.11ax/ac/b/g/n
    - 4*4 2.4G Wi-Fi standard   802.11b/g/n/ax
    - 4*4 5.8G Wi-Fi Standard   802.11 a/n/ac/ax
    - 2x 1 Gbps Ethernet (QCA8081) with 802.3at PoE input support
    - 1x  Reset
    - 1x  Bluetooth(optional)
    - 1x  DC Port 12V 3A
    - 4x Antenna    IPEX Connector, 3dBi omni antennas
    - Data Rate:    3657Mbps ( 2.4G: 1182Mbps (11ax 4x4); 5.8G: 2475Mbps (11ax 4x4))
    - RF Power: 2.4g ≤ 20dBm; 5.8g ≤ 19dBm
    - LED light:    Sys; 5.8G wifi; 2.4G wifi; WAN; LAN
    - Max Power Consumption:    ≤ 22W
    - Size: 198mm * 198mm * 41.02mm

BACKUP YOUR STOCK FIRMWARE:
```
export device=ax880
mkdir -p /tmp/fw_dump_$device
cd /tmp/fw_dump_$device
dmesg > dmesg_$device.log
dtc -I fs /sys/firmware/devicetree/base > $device.dts
cat /proc/device-tree/model > model
cat /proc/mtd > proc_mtd
while read p; do
mtd_dev=$(echo $p | cut -d: -f1)
echo $mtd_dev
dd if=/dev/$mtd_dev of=$mtd_dev
done < proc_mtd
md5sum * > md5sum.log
tar -cvzf ../$device.tar.gz .
export sum=$(md5sum /tmp/$device.tar.gz | cut -d' ' -f1)
mv ../$device.tar.gz /tmp/${device}_${sum}.tar.gz
echo fw backup saved to: /tmp/${device}_${sum}.tar.gz
```
Upload your backup via tftp to the safe place.

INSTALLATION:
1. stock firmware web ui
Rename factory.bin fw image file to factory.ubin. Flash this image
like ordinary stock fw upgrade.

2. stock firmware telnet method
Enter telnet cli (login: root, password: 476t*_f0%g09y) and upload
 factory.bin fw image and rename it to factory.ubin
`cd /tmp && wget <your_web_server_ip>/factory.ubin`
`sysupgrade factory.ubin

3. initramfs method
    Put openwrt-ipq807x-generic-yuncore_ax880-initramfs-uImage.itb to your
    TFTP server and rename it to ax880.initram
    Enable serial console and enter to the u-boot cli.
    Exec these commands:
    `tftpboot <your_tftp_server_ip>:ax880.initram`
    `dhcp`

    When downloading is finished:
    `bootm`
    After booting the device, you need to upload to the device factory.ubi fw image.
    ```
    cd /tmp && wget <your_web_server_ip>/factory.ubi`
    export rootfs=$(cat /proc/mtd | grep rootfs | cut -d: -f1)
    export rootfs_1=$(cat /proc/mtd | grep rootfs_1 | cut -d: -f1)
    ubiformat /dev/${rootfs} -y -f factory.ubi
    ubiformat /dev/${rootfs_1} -y -f factory.ubi
    reboot
    ```

4. u-boot factory.ubi image method
    Put openwrt-ipq807x-generic-yuncore_ax880-squashfs-factory.ubi to your
    TFTP server and rename it to ax880.ubi
    Enter u-boot cli and exec these commands:
    `tftpboot <your_tftp_server_ip>:ax880.ubi`
    `dhcp`
    After downloading is finished:
    `flash rootfs`
    `flash rootfs_1`
    `reset`

5. u-boot factory.bin method
    Put openwrt-ipq807x-generic-yuncore_ax880-squashfs-factory.bin to your
    TFTP server and rename it to ax880.bin
    Enter u-boot cli and exec these commands:
    `tftpboot <your_tftp_server_ip>:ax880.bin`
    `dhcp`
    After downloading is finished:
    `imgaddr=$fileaddr && nand device 0`
    Erase rootfs memory:
    `nand erase 0x00000000 0x03400000`
    Write rootfs:
    `nand write $fileaddr 0x00000000 $filesize`
    Erase rootfs_1 memory:
    `nand erase 0x3c00000 0x3400000`
    Write rootfs_1
    `nand write $fileaddr 0x3c00000 $filesize`
    `reset`

STOCK FIRMWARE RECOVERY:
Boot initramfs image.
Upload your rootfs mtd partition to the device using scp or download
it from the device using wget.
Enter device ssh cli and exec:
```
cd /tmp && wget <your_web_server_ip>/mtd21`
export rootfs=$(cat /proc/mtd | grep rootfs | cut -d: -f1)
export rootfs_1=$(cat /proc/mtd | grep rootfs_1 | cut -d: -f1)
ubiformat /dev/${rootfs} -y -f /tmp/mtd21
ubiformat /dev/${rootfs_1} -y -f /tmp/mtd21
reboot
```

Signed-off-by: Isaev Ruslan <legale.legale@gmail.com>
Reviewed-by: Robert Marko <robimarko@gmail.com>