docs: dt: submitting-patches: Document sending DTS patches

docs: dt: submitting-patches: Document sending DTS patches

Document two rules already widely used and enforced by DT maintainers
and SoC platform maintainers:

1. DTS patches should be placed at the end of driver patchset to
   indicate no dependencies of driver code on DTS.

2. DTS patches should be applied via SoC platform maintainers, because
   it is a driver-independent hardware description.  However some
   driver maintainers are reluctant to pick up portions of patchsets and
   prefer to take entire set at once.  For such cases, the DTS portion
   should be split into separate patchset, so it will not end up in the
   driver subsystem integration tree.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://lore.kernel.org/r/20250225184822.213296-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>