mediatek: make use of common uImage.FIT upgrade functions

Use newly introduced fit_do_upgrade() function in /lib/upgrade/platform.sh.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

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

@@ -12,25 +12,8 @@ platform_do_upgrade() {
 	ubnt,unifi-6-lr-v2-ubootmod|\
 	ubnt,unifi-6-lr-v3-ubootmod|\
 	xiaomi,redmi-router-ax6s)
-		[ -e /dev/fit0 ] && fitblk /dev/fit0
-		[ -e /dev/fitrw ] && fitblk /dev/fitrw
-		bootdev="$(fitblk_get_bootdev)"
-		case "$bootdev" in
-		mmcblk*)
-			EMMC_KERN_DEV="/dev/$bootdev"
-			emmc_do_upgrade "$1"
-			;;
-		mtdblock*)
-			PART_NAME="/dev/mtd${bootdev:8}"
-			default_do_upgrade "$1"
-			;;
-		ubiblock*)
-			CI_KERNPART="fit"
-			nand_do_upgrade "$1"
-			;;
-		esac
+		fit_do_upgrade "$1"
 		;;
-
 	buffalo,wsr-2533dhp2|\
 	buffalo,wsr-3200ax4s)
 		local magic="$(get_magic_long "$1")"