dt-bindings: net: Define properties at top-level

Convention is DT schemas should define all properties at the top-level
and not inside of if/then schemas. That minimizes the if/then schemas
and is more future proof.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Link: https://patch.msgid.link/20240703195827.1670594-2-robh@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>