ramips: add support for I-O DATA WN-AC733GR3

I-O DATA WN-AC733GR3 is a 2.4/5 GHz band 11ac router, based on
MediaTek MT7620A.

Specification

- SoC		: MediaTek MT7620A
- RAM		: DDR2 64 MiB
- Flash		: SPI-NOR 8 MiB
- WLAN		: 2.4/5 GHz
  - 2.4 GHz : MT7620A (SoC), 2T2R
  - 5 GHz   : MT7610E, 1T1R
- Ethernet	: 10/100/1000 Mbps (RTL8367RB)
- LED/key	: 4x/4x (2x buttons, 1x slide-switch)
- UART		: through-hole on PCB
  - J1: Vcc, RX, GND, TX from LED side
  - 57600n8

Flash instruction using factory image:

1. Boot WN-AC733GR3 normaly
2. Access to "http://192.168.0.1/" and open firmware update page
("ファームウェア")
3. Select the OpenWrt factory image and click update ("更新") button
to perform firmware update
4. Wait ~150 seconds to complete flashing

Signed-off-by: INAGAKI Hiroshi <musashino.open@gmail.com>

target/linux/ramips/base-files/etc/board.d/01_leds

@@ -196,7 +196,8 @@ ht-tm02)
 	ucidef_set_led_netdev "eth" "Ethernet" "$boardname:green:lan" "eth0"
 	set_wifi_led "$boardname:blue:wlan"
 	;;
-iodata,wn-ac1167gr)
+iodata,wn-ac1167gr|\
+iodata,wn-ac733gr3)
 	ucidef_set_led_wlan "wlan5g" "WLAN5G" "$boardname:green:wlan5g" "phy0radio"
 	ucidef_set_led_wlan "wlan2g" "WLAN2G" "$boardname:green:wlan2g" "phy1radio"
 	;;

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

@@ -324,7 +324,8 @@ ramips_setup_interfaces()
 		ucidef_add_switch "switch0" \
 			"0:lan" "1:lan" "5:wan" "6@eth0"
 		;;
-	iodata,wn-ac1167gr)
+	iodata,wn-ac1167gr|\
+	iodata,wn-ac733gr3)
 		ucidef_add_switch "switch1" \
 			"1:lan:4" "2:lan:3" "3:lan:2" "4:lan:1" "0:wan" "6@eth0"
 		;;
@@ -546,7 +547,8 @@ ramips_setup_macs()
 		[ -n "$lan_mac" ] || lan_mac=$(cat /sys/class/net/eth0/address)
 		wan_mac=$(macaddr_add "$lan_mac" 1)
 		;;
-	iodata,wn-ac1167gr)
+	iodata,wn-ac1167gr|\
+	iodata,wn-ac733gr3)
 		wan_mac=$(macaddr_add "$(mtd_get_mac_binary Factory 4)" -1)
 		;;
 	iodata,wn-ax1167gr|\