Add (Horaco) ZX310S-4T2XT

The ZX310S-4T2XT is a managed device with 2x2.5GBit and 2x10GBit Ethernet.
It is sold, among others, by Horaco as an unbranded device.

CPU: RTL8372
Flash: 2MByte Winbond W25Q16DV (U3)
PHY 2x RTL8261BE

doc/devices/ZX310S-4T2XT.md

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+# ZX310S-4T2XT
+
+The following is a documentation for the managed switch marked as
+`ZX310S-4T2XT` and sold by Horaco.
+
+The original software is running UART on 57600 baud rate 8N1.
+
+CPU: RTL8372
+Flash: 2MByte Winbond W25Q16DV (U3)
+PHY 2x RTL8261BE
+
+### Label specifications
+
+- **Name**:
+- **Ports**:
+  - 4 × RJ45: 10/100/1000/2500 Mbps
+  - 2 x RJ45: 10/100/1000/2500/5000/10000 Mbps
+- **Power**: 12V DC, 2A barrel connector
+
+<img src="photos/ZX310S-4T2XT/label.jpg" width="300" />
+
+### What works
+The device is fully supported:
+- All 4 2.5GBASE-T RJ45 ports work at 10/100/1000/2500 Mbps, including EEE
+- The 10GBit ports works, including EEE.
+- LEDs work with the same indiciations as the OEM firmware
+
+### PCB overview
+
+**Board markings**
+- Top silkscreen: PCB-SL310S-4T2XT-V1.0.0-22273
+
+Top side
+
+<img src="photos/ZX310S-4T2XT/pcb_top.jpg" width="300" />
+
+Bottom
+
+<img src="photos/ZX310S-4T2XT/pcb_bottom.jpg" width="300" />
+
+### J1, serial console
+
+| `J1` pin | Signal      |
+| -------- | ----------- |
+| 1        | TX (Output) |
+| 2        | RX (Input)  |
+| 3        | GND         |
+| 4        | 3V3         |
+
+
+## Power supply
+
+Input power is delivered via barell plug, `12V 2A` adapter was provided.