uboot-envtools: mvebu: update uci defaults for Turris Omnia

From version 2021.09 U-Boot will fixup Turris Omnia's DTB before
booting, separating U-Boot's environment into separate MTD partition
"u-boot-env" [1].

Check if "u-boot-env" MTD partition exists and set the uci defaults
accordingly.

[1] https://lists.denx.de/pipermail/u-boot/2021-July/455017.html

Signed-off-by: Marek Behún <marek.behun@nic.cz>

package/boot/uboot-envtools/files/mvebu

@@ -17,7 +17,10 @@ buffalo,ls421de)
 	ubootenv_add_uci_config "/dev/mtd3" "0x0" "0x10000"
 	;;
 cznic,turris-omnia)
-	if grep -q 'U-Boot 2015.10-rc2' /dev/mtd0; then
+	idx="$(find_mtd_index u-boot-env)"
+	if [ -n "$idx" ]; then
+		ubootenv_add_uci_config "/dev/mtd${idx}" "0x0" "0x10000" "0x10000"
+	elif grep -q 'U-Boot 2015.10-rc2' /dev/mtd0; then
 		ubootenv_add_uci_config "/dev/mtd0" "0xc0000" "0x10000" "0x40000"
 	else
 		ubootenv_add_uci_config "/dev/mtd0" "0xf0000" "0x10000" "0x10000"