ramips: add support for Mercusys MR70X

Hardware
========
- SoC: MediaTek MT7621AT (880MHz, Duel-Core)
- RAM: DDR3 128MB
- Flash: Winbond W25Q128JV (SPI-NOR 16MB)
- WiFi: MediaTek MT7915D (2.4GHz, 5GHz, DBDC)
- Ethernet: MediaTek MT7530 (WAN x1, LAN x3, SoC)
- UART: >TX RX GND 3v3 (115200 8N1, J1)
        Do not connect 3v3. TX is marked with an arrow.

Installation
============
Flash factory image. This can be done using stock web ui.

Revert to stock firmware
========================
Flash stock firmware via OEM Web UI Recovery mode.

Web UI Recovery method
======================
1. Unplug the router
2. Plug in and hold reset button 5~10 secs
3. Set your computer IP address manually to 192.168.1.x / 255.255.255.0
4. Flash image with web browser to 192.168.1.1

Co-authored-by: Robert Senderek <robert.senderek@10g.pl>
Co-authored-by: Yoonji Park <koreapyj@dcmys.kr>
Signed-off-by: David Bauer <mail@david-bauer.net>

target/linux/ramips/mt7621/base-files/etc/hotplug.d/ieee80211/10_fix_wifi_mac

@@ -120,6 +120,11 @@ case "$board" in
 		[ "$PHYNBR" = "0" ] && macaddr_add $hw_mac_addr 2 > /sys${DEVPATH}/macaddress
 		[ "$PHYNBR" = "1" ] && macaddr_add $hw_mac_addr 3 > /sys${DEVPATH}/macaddress
 		;;
+	mercusys,mr70x-v1|\
+	tplink,archer-ax23-v1)
+		hw_mac_addr="$(mtd_get_mac_binary config 0x8)"
+		[ "$PHYNBR" = "1" ] &&  macaddr_add "$hw_mac_addr" -1 > "/sys${DEVPATH}/macaddress"
+		;;
 	mts,wg430223)
 		hw_mac_addr=$(macaddr_add $(mtd_get_mac_encrypted_arcadyan "board_data") 1)
 		[ "$PHYNBR" = "0" ] && echo -n "$hw_mac_addr" > /sys${DEVPATH}/macaddress
@@ -147,10 +152,6 @@ case "$board" in
 		hw_mac_addr="$(mtd_get_mac_binary factory 0x4)"
 		[ "$PHYNBR" = "1" ] &&  macaddr_add $hw_mac_addr "0x100000" > /sys${DEVPATH}/macaddress
 		;;
-	tplink,archer-ax23-v1)
-		hw_mac_addr="$(mtd_get_mac_binary config 0x8)"
-		[ "$PHYNBR" = "1" ] &&  macaddr_add "$hw_mac_addr" -1 > "/sys${DEVPATH}/macaddress"
-		;;
 	tplink,eap615-wall-v1)
 		hw_mac_addr="$(mtd_get_mac_binary product-info 0x8)"
 		macaddr_add "$hw_mac_addr" "$PHYNBR" > "/sys${DEVPATH}/macaddress"