ramips: add support for ipTIME A604M

ipTIME A604M is a 2.4/5GHz band AC1200 router, based on MediaTek
MT7628AN.

Specifications:
- SoC: MT7628AN
- RAM: DDR2 64MB
- Flash: SPI NOR 8MB
- WiFi:
  - 2.4GHz: SoC internal
  - 5GHz: MT7612EN
- Ethernet: 5x 10/100Mbps
  - Switch: SoC internal
- UART:
  - J1: 3.3V, TX, RX, GND (3.3V is the square pad) / 57600 8N1

Installation via web interface:
1.  Flash **initramfs** image through the stock web interface.
2.  Boot into OpenWrt and perform sysupgrade with sysupgrade image.

Revert to stock firmware:
1.  Perform sysupgrade with stock image.

Signed-off-by: Sungbo Eo <mans0n@gorani.run>

target/linux/ramips/base-files/etc/board.d/02_network

@@ -305,7 +305,8 @@ ramips_setup_interfaces()
 	elecom,wrc-2533gst|\
 	huawei,hg255d|\
 	iodata,wn-ax1167gr|\
-	iodata,wn-gx300gr)
+	iodata,wn-gx300gr|\
+	iptime,a604m)
 		ucidef_add_switch "switch0" \
 			"1:lan:4" "2:lan:3" "3:lan:2" "4:lan:1" "0:wan" "6@eth0"
 		;;
@@ -616,6 +617,9 @@ ramips_setup_macs()
 	trendnet,tew-692gr)
 		wan_mac=$(macaddr_add "$(mtd_get_mac_binary factory 0x4)" 1)
 		;;
+	iptime,a604m)
+		wan_mac=$(mtd_get_mac_binary u-boot 0x1fc40)
+		;;
 	lenovo,newifi-d1)
 		lan_mac=$(macaddr_add "$(cat /sys/class/net/eth0/address)" 2)
 		;;