[][Refactor mt7981 dts/image naming rule]

[Description]
Refactor mt7981 dts/image naming rule

[Release-log]
N/A

Change-Id: I2e62091d89df4e12871237b5b47765a85210539f
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/5266015
5 files changed