ramips: add support for TP-Link RE205 v2

[baslogic]

Summary

Add OpenWrt support for the TP-Link RE205 v2 range extender.

The RE205 v2 is a dual-band (2.4GHz + 5GHz) range extender based on the
MT7628AN + MT7610E chipset. It shares the same hardware platform as the
already-supported RE205 v3 and RE200 v4, but with a different board ID
and product version in the TP-Link safeloader format.

Hardware

• SoC: MediaTek MT7628AN (MIPS 24KEc @ 580MHz)
• RAM: 64MB
• Flash: 8MB
• 2.4GHz: MT7628 802.11b/g/n HT20 (2T2R)
• 5GHz: MT7610E 802.11a/n/ac VHT80 (1T1R, PCIe)
• Ethernet: 1x 10/100 Mbps
• LEDs: 5x (power, signal blue, signal red, 2.4GHz, 5GHz)
• Button: WPS/Reset (GPIO 38)

Changes

• DTS: New device tree based on mt7628an_tplink_re200.dtsi with blue LED GPIO mapping (39-43), identical to RE205 v3
• tplink-safeloader: Board entry with 13 special_id entries extracted from stock firmware, partition table identical to RE200 v4 and RE205 v3
• Image definition: 7808k image size, kmod-mt76x0e for 5GHz PCIe radio
• board.d: LED and network entries grouped with RE205 v3

Testing

• Built and flashed successfully (both factory from stock firmware and sysupgrade)
• Tested on OpenWrt 24.10.5 and snapshot
• 2.4GHz and 5GHz radios working, 18+ clients stable
• LuCI accessible, all LEDs functional
• Sysupgrade with and without config preservation verified
• Performance validated: MCS 5-7 TX rates, 90% CPU idle, no driver errors

Installation

Flash via stock TP-Link web UI using the factory image, or via TFTP recovery
(hold reset during power-on, device at 192.168.1.1, TFTP server at 192.168.1.66,
firmware renamed to test.bin — see RE200 wiki).

[mrkiko]

If you want, you might also add that it requires firmware to be renamed to tp_recovery.bin, if this is the case.

[baslogic]

Thanks for the suggestion! For this device family (RE200/RE205), the TFTP recovery filename is actually test.bin, not tp_recovery.bin. I've updated the PR description to include this.

Reference: https://openwrt.org/toh/tp-link/re200

[baslogic]

Moved the tplink-safeloader board entry to a separate firmware-utils PR as requested:
openwrt/firmware-utils#61

This PR now only contains the DTS, image definition, and board.d entries.
The firmware-utils patch has been removed.