ramips: add support for ipTIME A3

ipTIME A3 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: 3x 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

@@ -376,6 +376,10 @@ ramips_setup_interfaces()
 		ucidef_add_switch "switch1" \
 			"1:lan:4" "2:lan:3" "3:lan:2" "4:lan:1" "0:wan" "6@eth0"
 		;;
+	iptime,a3)
+		ucidef_add_switch "switch0" \
+			"2:lan:2" "3:lan:1" "0:wan" "6@eth0"
+		;;
 	lava,lr-25g001|\
 	sitecom,wlr-6000|\
 	trendnet,tew-691gr|\
@@ -666,6 +670,7 @@ ramips_setup_macs()
 	trendnet,tew-692gr)
 		wan_mac=$(macaddr_add "$(mtd_get_mac_binary factory 0x4)" 1)
 		;;
+	iptime,a3|\
 	iptime,a604m)
 		wan_mac=$(mtd_get_mac_binary u-boot 0x1fc40)
 		;;