docs: dt-bindings: add DTS Coding Style document

docs: dt-bindings: add DTS Coding Style document

Document preferred coding style for Devicetree sources (DTS and DTSI),
to bring consistency among all (sub)architectures and ease in reviews.

Cc: Andrew Davis <[email protected]>
cc: Andrew Lunn <[email protected]>
Cc: AngeloGioacchino Del Regno <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Bjorn Andersson <[email protected]>
Cc: Chen-Yu Tsai <[email protected]>
Cc: Dmitry Baryshkov <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Matthias Brugger <[email protected]>
Cc: Michal Simek <[email protected]>
Cc: Neil Armstrong <[email protected]>
Cc: Nishanth Menon <[email protected]>
Cc: Olof Johansson <[email protected]>
Cc: Rafał Miłecki <[email protected]>
Acked-by: Neil Armstrong <[email protected]>
Acked-by: Heiko Stuebner <[email protected]>
Reviewed-by: Laurent Pinchart <[email protected]>
Acked-by: Konrad Dybcio <[email protected]>
Reviewed-by: Geert Uytterhoeven <[email protected]>
Signed-off-by: Krzysztof Kozlowski <[email protected]>
Reviewed-by: Conor Dooley <[email protected]>
Reviewed-by: Francesco Dolcini <[email protected]>
Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[robh: quote property names in order of properties section]
Signed-off-by: Rob Herring <[email protected]>