ramips: add support for Edimax BR-6478AC v2

Roll-up of patches by Rohan Murch, Hans Ulli Kroll, and James McKenzie.
Taken from https://forum.openwrt.org/viewtopic.php?id=67192 and updated.

Specification:
- System-On-Chip: MT7620A
- CPU/Speed: 580 MHz
- Flash-Chip: Macronix MX25L6405D
- Flash size: 8192 KiB
- RAM: 64 MiB
- Wireless No1: SoC-integrated: MT7620A 2.4GHz 802.11bgn
- Wireless No2: On-board chip: MT7612E 5GHz 802.11ac
- Switch: Mediatek MT7530W Gigabit Switch
- USB: Yes 1 x 2.0

Installation:
1. Download sysupgrade.bin
2. Open vendor web interface
3. Choose to upgrade firmware
4. After reboot connect via ethernet at 192.168.1.1

Signed-off-by: Daniel Gimpelevich <daniel@gimpelevich.san-francisco.ca.us>

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

@@ -86,6 +86,12 @@ asl26555-16M)
 bc2)
 	set_usb_led "$boardname:blue:usb"
 	;;
+br-6478ac-v2)
+	ucidef_set_led_default "power" "POWER" "$boardname:white:power" "1"
+	ucidef_set_led_netdev "wan" "wan" "$boardname:blue:wan" "eth0.2"
+	set_wifi_led "$boardname:blue:wlan"
+	set_usb_led "$boardname:blue:usb"
+	;;
 broadway)
 	set_usb_led "$boardname:red:diskmounted"
 	set_wifi_led "$boardname:red:wps_active"

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

@@ -341,6 +341,7 @@ ramips_setup_interfaces()
 		ucidef_add_switch "switch0" \
 			"1:lan" "2:lan" "3:lan" "4:lan" "5:wan" "0@eth0"
 		;;
+	br-6478ac-v2|\
 	tplink,c2-v1)
 		ucidef_add_switch "switch1" \
 			"1:lan" "2:lan" "3:lan" "4:lan" "0:wan" "6@eth0"
@@ -446,6 +447,10 @@ ramips_setup_macs()
 		lan_mac=$(cat /sys/class/net/eth0/address)
 		wan_mac=$(mtd_get_mac_binary devdata 7)
 		;;
+	br-6478ac-v2)
+		lan_mac=$(cat /sys/class/net/eth0/address)
+		wan_mac=$(macaddr_add "$lan_mac" 2)
+		;;
 	cy-swr1100|\
 	dch-m225)
 		lan_mac=$(mtd_get_mac_ascii factory lanmac)