docs: dt-bindings: Document preferred line wrapping

There are some patches with long lines as a result of checkpatch
enforcing 100, not 80, but checkpatch is only a tool not a coding style.
The Linux Kernel Coding Style is still clear here on preferred limit.
Mentioned preferred style of wrapping long lines in DTS, based on Linux
Kernel Coding Style.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20250118102247.18257-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Rob Herring (Arm) <robh@kernel.org>