lantiq: move device tree files to target dts directory
In this target, we only use downstream dts files. And it doesn't
seem like there will be significant changes upstream. Move dts files
to the target dts folder to avoid copying them over and over again
during annual kernel upgrades.
Signed-off-by: Shiji Yang <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/22876
Signed-off-by: Robert Marko <[email protected]>