mediatek: add support for ipTIME AX3000SE

mediatek: add support for ipTIME AX3000SE

Specification
-------------
- SoC       : MediaTek MT7981BA dual-core ARM Cortex-A53 1.3GHz
- RAM       : DDR3 256Mbytes, ESMT M15T2G16128A
- Flash     : 128Mbytes NAND Flash, ESMT F50L1G41LB
- WLAN      : MediaTek MT7976CN dual-band Wi-Fi 6
  - 2.4GHz  : b/g/n/ax, MU-MIMO
  - 5GHz    : a/n/ac/ax, MU-MIMO
- Ethernet  : MediaTek MT7531AE
  - LAN     : 10/100/1000 Mbps x4
  - WAN     : 10/100/1000 Mbps x1
- UART      : 1x4 pin header hole on PCB
  - 3.3V, RX, GND, TX (115200, 8N1)
- Buttons   : WPS, Reset
- LEDs      : 1x CPU (Amber/Blue)
              1x Wi-Fi (Amber/Blue)
              1x WAN activity (Amber/Blue)
              4x LAN activity (Amber/Blue)
- Power     : 12VDC, 1A (Center positive polarity)

Note: The LED color is amber or blue, depending on your router's color
(black/white).

MAC address
-----------
+-----------+-------------------+-----------+
| Interface | MAC               | Algorithm |
+-----------+-------------------+-----------+
| WLAN 2.4G | B0:38:6C:xx:xx:xx | label     |
| WLAN 5G   | B2:38:6C:4x:xx:xx |           |
| WAN       | B0:38:6C:xx:xx:xx | label + 1 |
| LAN       | B0:38:6C:xx:xx:xx | label + 3 |
+-----------+-------------------+-----------+
The WLAN 2.4G MAC address was found in 'Factory' partition, 0x4

Installation
------------
1. Download the OEM recovery software (ipTIME Firmware Wizard (11ac))
   from the manufacturer's website
2. Download the *squashfs-factory.bin file from the OpenWrt website
3. Press a reset button, and power up the router (keep pressing the reset button)
4. Wait more than 10 seconds until the CPU LED stop blinking
5. Connect the router (LAN port) to the PC
6. Run the OEM recovery software and follow the instructions
7. Select the *squashfs-factory.bin file during the router recovery process
8. Wait for the router to boot from *squashfs-factory.bin

Limitation: Triggering the WLAN LED for activity on both phy0 (2.4GHz) and phy1 (5GHz)
----------
Currently, the UCI doesn't support triggering a single LED for activity
on multiple WLAN interfaces. As a temporary workaround, the LED is
configured to only indicate activity on `phy1`. If you wish to monitor
`phy0` instead, you must change the device from `phy1-ap0` to `phy0-ap0`
in the LuCI LED configuration.

Signed-off-by: Donghyun Ko <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/20771
Signed-off-by: Hauke Mehrtens <[email protected]>