mediatek: add support for TOTOLINK A8000RU

Specifications:
- SoC: MT7622
- RAM: 512MB
- Flash: MX35LF1GE4AB 128MB SPI NAND
- Ethernet: RTL8367S 5x1GbE
- WiFi: 2.4G: MT7622 5G: MT7615N x2
- Other ports: USB3.0 x1

Flash instruction:
*important*: upgrade vendor firmware to at least V7.1cu.643_B20200521
1. hold the reset button and power on the device. wait for about 10s
   before releasing the reset button.
2. upload sysupgrade.bin via u-boot recovery page on http://192.168.1.1

Signed-off-by: Chuanhong Guo <gch981213@gmail.com>

target/linux/mediatek/mt7622/base-files/lib/upgrade/platform.sh

@@ -54,6 +54,9 @@ platform_do_upgrade() {
 		fi
 		default_do_upgrade "$1"
 		;;
+	totolink,a8000ru)
+		nand_do_upgrade "$1"
+		;;
 	*)
 		default_do_upgrade "$1"
 		;;
@@ -72,6 +75,9 @@ platform_check_image() {
 	buffalo,wsr-2533dhp2)
 		buffalo_check_image "$board" "$magic" "$1" || return 1
 		;;
+	totolink,a8000ru)
+		nand_do_platform_check "$board" "$1"
+		;;
 	*)
 		[ "$magic" != "d00dfeed" ] && {
 			echo "Invalid image type."