dt-bindings: serial: Convert socionext,milbeaut-usio-uart to DT schema

Convert the Socionext Milbeaut UART binding to DT schema. It is a
straight-forward conversion.

Reviewed-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: "Rob Herring (Arm)" <robh@kernel.org>
Link: https://lore.kernel.org/r/20250507154924.1602842-1-robh@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>