ramips-mt76x8: add support for TP-Link RE200 v2 (#2275)

TP-Link RE200 v2 is a wireless range extender with Ethernet and 2.4G and 5G
WiFi with internal antennas. It's based on MediaTek MT7628AN+MT7610EN.

Specifications
--------------

- MediaTek MT7628AN (580 Mhz)
- 64 MB of RAM
- 8 MB of FLASH
- 2T2R 2.4 GHz and 1T1R 5 GHz
- 1x 10/100 Mbps Ethernet
- UART header on PCB (57600 8n1)
- 8x LED (GPIO-controlled), 2x button

There are 2.4G and 5G LEDs in red and green which are controlled
separately.

MAC addresses
-------------

The MAC address assignment matches stock firmware, i.e.:
LAN : *:0D
2.4G: *:0E
5G  : *:0F

Installation
------------

Web Interface
-------------

It is possible to upgrade to OpenWrt via the web interface. Simply flash
the -factory.bin from OEM. In contrast to a stock firmware, this will not
overwrite U-Boot.

docs/user/supported_devices.rst

@@ -210,7 +210,7 @@ ramips-mt7621
 
   - WG3526-16M
   - WG3526-32M
-  
+
 * Xiaomi
 
   - Xiaomi Mi Router 4A (Gigabit Edition)
@@ -239,6 +239,7 @@ ramips-mt76x8
 
   - Archer C50 (v3)
   - Archer C50 (v4)
+  - RE200 (v2)
   - TL-MR3020 (v3)
   - TL-MR3420 (v5)
   - TL-WA801ND (v5)

targets/ramips-mt76x8

@@ -39,6 +39,8 @@ device('tp-link-archer-c50-v4', 'tplink_archer-c50-v4', {
 	factory = false,
 })
 
+device('tp-link-re200-v2', 'tplink_re200-v2')
+
 device('tp-link-tl-mr3020-v3', 'tplink_tl-mr3020-v3', {
 	factory = false,
 	extra_images = {