dt-bindings: serial: Add bindings doc for Sunplus SoC UART Driver

Add bindings doc for Sunplus SoC UART Driver

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hammer Hsieh <hammerh0314@gmail.com>
Link: https://lore.kernel.org/r/1645522563-17183-2-git-send-email-hammerh0314@gmail.com


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