layerscape: armv8_64b: traverse ten64-mtd fix ASU support

The profiles.json[1] in generated and used during ASU sysupgrades takes
DEVICE_NAME as profile name which break ASU sysupgrades, use BOARD_NAME
which serves the same goal as overwriting DEVICE_NAME, allowing
sysupgrade-tar's checks be succesfully passed using the old name used in
older installations. Without affecting the generated profiles.json, thus
recovering ASU support.

*Keep the non-stardand device name with suffix "-mtd"(replaced underscore
by hyphen) to remark that this device is also supported in the armsr
(armvirt) target as originally intented[2].
*I think I have fully checked the sysupgrade path to confirm this change
does not have side effects.

[1]: https://downloads.openwrt.org/releases/25.12.0/targets/layerscape/armv8_64b/profiles.json
[2]: openwrt/openwrt#12828
Fixes: af0546d ("layerscape: armv8_64b: add Traverse Ten64 NAND variant")
Fixes: openwrt/asu#1583

Reported-by: DanaGoyette (github)
Co-developed-by: Eric Fahlgren <ericfahlgren@gmail.com>
Signed-off-by: Mario Andrés Pérez <mapb_@outlook.com>
Link: openwrt/openwrt#22359
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

Author: map-b

target/linux/layerscape/image/armv8_64b.mk

@@ -375,10 +375,10 @@ define Device/fsl_lx2160a-rdb-sdboot
 endef
 TARGET_DEVICES += fsl_lx2160a-rdb-sdboot
 
-define Device/traverse_ten64_mtd
+define Device/traverse_ten64-mtd
   DEVICE_VENDOR := Traverse
   DEVICE_MODEL := Ten64 (NAND boot)
-  DEVICE_NAME := ten64-mtd
+  BOARD_NAME := ten64-mtd
   DEVICE_PACKAGES += \
     uboot-envtools \
     kmod-rtc-rx8025 \
@@ -404,5 +404,5 @@ define Device/traverse_ten64_mtd
   MKUBIFS_OPTS := -m $$(PAGESIZE) -e 124KiB -c 600
   SUPPORTED_DEVICES = traverse,ten64
 endef
-TARGET_DEVICES += traverse_ten64_mtd
+TARGET_DEVICES += traverse_ten64-mtd