dt-bindings: serial: renesas,scif: Move ref for serial.yaml at the end

dt-bindings: serial: renesas,scif: Move ref for serial.yaml at the end

In preparation for adding more validation checks move the ref for
'serial.yaml' to the end and also move reset check in 'allOf' block.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240604170513.522631-2-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>