doc: dts: explain how to view preprocessor output

   	clock-frequency = <115200>;

   };

Look at the preprocessor output

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To save preprocessor output when using GCC-based toolchains, add

``-save-temps=obj`` to the ``EXTRA_CFLAGS`` CMake variable. For example, to

build :ref:`hello_world` with west with this option set, use:

.. code-block:: sh

   west build -b BOARD samples/hello_world -- -DEXTRA_CFLAGS=-save-temps=obj

This will create a preprocessor output file named :file:`foo.c.i` in the build

directory for each source file :file:`foo.c`.

You can then search for the file in the build directory to see what your

devicetree macros expanded to. For example, on macOS and Linux, using ``find``

to find :file:`main.c.i`:

.. code-block:: sh

   $ find build -name main.c.i

   build/CMakeFiles/app.dir/src/main.c.i

It's usually easiest to run a style formatter on the results before opening

them. For example, to use ``clang-format`` to reformat the file in place:

.. code-block:: sh

   clang-format -i build/CMakeFiles/app.dir/src/main.c.i

You can then open the file in your favorite editor to view the final C results

after preprocessing.

Validate properties

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