mediatek: mt7623: get rid of fitblk_get_bootdev

Also migrate mt7623 to new fitblk support scripts which simplify
sysupgrade when using uImage.FIT. This had been forgotten previously.

Fixes: 4448d6325f ("mediatek: make use of common uImage.FIT upgrade functions")
Signed-off-by: Daniel Golle <daniel@makrotopia.org>

target/linux/mediatek/mt7623/base-files/lib/upgrade/platform.sh

@@ -1,4 +1,5 @@
 REQUIRE_IMAGE_METADATA=1
+RAMFS_COPY_BIN='fitblk'
 
 # Legacy full system upgrade including preloader for MediaTek SoCs on eMMC or SD
 legacy_mtk_mmc_full_upgrade() {
@@ -83,11 +84,7 @@ platform_do_upgrade() {
 	case "$board" in
 	bananapi,bpi-r2|\
 	unielec,u7623-02)
-		[ -e /dev/fit0 ] && fitblk /dev/fit0
-		[ -e /dev/fitrw ] && fitblk /dev/fitrw
-		bootdev="$(fitblk_get_bootdev)"
-		EMMC_KERN_DEV="/dev/$bootdev"
-		emmc_do_upgrade "$1"
+		fit_do_upgrade "$1"
 		;;
 	unielec,u7623-02-emmc-512m)
 		local magic="$(get_magic_long "$1")"