doc: add Sirivision SR-S25G2109F (S25G1109FP V1.3)

Device page following doc/adding-a-device.md: label data, PCB versus label
naming, CPU identified with 'regget 4' (RTL8373, non-N), separate PHY and flash
identification, build target, PCB silkscreen, port mapping, board signals, front
panel and LED configuration, reset button, MAC location, what works and what is
unverified, plus photos.  Row added to supported_devices.md.

doc/supported_devices.md

@@ -42,6 +42,7 @@ The following devices have been tested and are fully working:
 | Ruiying  | RY-4GT-2SX      | No      | [FG-4GT-2SX_V2.0](devices/FG-4GT-2SX_V2.0.md)                             | 4M    | 4 + 2 |
 | Ruiying  | RY-8GT-1SX      | No      | [FG-8GT-1SX](devices/FG-8GT-1SX.md)                                       | 1M    | 8 + 1 |
 | SICSOLINK| SL-G0402F       | No      | [PCB-K0402WS-V3.0](devices/PCB-K0402WS-V3.0.md)                           |       | 4 + 2 |
+| Sirivision | SR-S25G2109F  | Yes     | [S25G1109FP V1.3](devices/S25G1109FP_V1_3.md)                             | 2M    | 8 + 1 |
 | Sodola   | SL-SWTG124AS-D  | Yes     | [SWTG024AS-v2.0-17452](devices/SWTG024AS.md)                              | 2M    | 4 + 2 |
 | Steamemo | IG204-V1        | No      | [PB-2131](devices/STEAMEMO_IG204_V1.md)                                   |       | 4 + 2 |
 | TRENDnet | TEG-S562        | No      | [TEG-S563/EU H/W: V1.0R](devices/TEG-S562.md)                             | 2M    | 4 + 2 |