cmake: extensions: Add TARGET arguments to the dt_* API

The CMake dt_* API is backed by target properties. By default, it uses
the target named `devicetree_target` that is initialized in `dts.cmake`.

We should be able to customize this, now that we have a function for
loading those properties into a different target. For example:

    zephyr_dt_import(EDT_PICKLE_FILE /path/to/edt.pickle TARGET target)

    dt_nodelabel(node NODELABEL label TARGET target)

This would make it possible to reference multiple devicetrees in the
same build system, particularly sysbuild.

Signed-off-by: Grzegorz Swiderski <[email protected]>

Author: 57300