ipq40xx: add support for SKSpruce WIA3300-20

ipq40xx: add support for SKSpruce WIA3300-20

Specification
-------------
- SoC       : Qualcomm IPQ4019
- RAM       : 256 MiB DDR3 (NT5CC128M16JR-EK)
- Flash     : 64 MiB SPI NOR (Winbond W25Q512JVFQ)
- WLAN      : IPQ4019 built-in
  - 2.4 GHz : 2x2 MIMO WiFi4
  - 5 GHz   : 2x2 MIMO WiFi5
- Ethernet  : QCA8075 10/100/1000 Mbps 1x WAN (ETH1, PoE); 1x LAN (ETH2)
- USB       : 1x 2.0 Type-A
- UART      : 3.3V, 115200n8
- Buttons   : 1x Reset
- LEDs      : 1x RUN (lime & red)
              1x WiFi 2.4 GHz (lime)
              1x WiFi 5 GHz (lime)
              2x ETH (lime), controlled by the QCA8075 phy
- Power     : DC 12V & 802.3at PoE
- FCC ID    : 2AHKT-WIA3300-20
- TFTP IP   :
  - client  : 192.168.18.254
  - router  : 192.168.18.1

Installation
------------
1. Open uart console and start TFTP server. Copy initramfs image to
   the TFTP root directory and rename it to 'ipqinitramfs.bin'.
2. Power on and press 'Enter' to exit to the u-boot console according
   to the TTL log prompt.
3. Execute commands to load the initramfs image:
   tftpboot && bootm
4. Enter into OpenWrt to backup the partitions if you want to restore
   the stock firmware one day.
5. Override default 'bootcmd' environment variable in u-boot console:
   env set bootcmd 'sf probe && sf read $loadaddr 0x980000 0x800000 && bootm $loadaddr'
   env save
6. Repeat step 3 and flash 'sysupgrade' image in OpenWrt.

Recovery and return to stock
----------------------------
1. Restore the backup firmware partitions in the installation step 4.
2. Restore `bootcmd` environment variable via commands:
   env set bootcmd bootipq && env save

MAC addresses
-------------
+---------+-------------------+
|         | MAC example       |
+---------+-------------------+
| LABEL   | xx:xx:xx:xx:xx:25 |
| LAN     | xx:xx:xx:xx:xx:26 |
| WAN     | xx:xx:xx:xx:xx:25 |
| WLAN 2g | xx:xx:xx:xx:xx:28 |
| WLAN 5g | xx:xx:xx:xx:xx:29 |
+---------+-------------------+

Notice
-----------
1. Some CH340 USB-TTL module doesn't work on this device.
2. The 'firmware' partition consists of four parts in the vendor
   layout:
     * Name            Start           Size
     * rootfs          0x980000        0x1680000
     * 0:HLOS1         0x2000000       0x800000
     * rootfs_1        0x2800000       0x1400000
     * rootfs_data     0x3c00000       0x350000
3. User can control the USB power supply via commands:
   echo enabled > /sys/devices/platform/output-usb-power/state
   echo disabled > /sys/devices/platform/output-usb-power/state

Signed-off-by: Shiji Yang <yangshiji66@qq.com>
Link: https://github.com/openwrt/openwrt/pull/16476
Signed-off-by: Robert Marko <robimarko@gmail.com>