dt-bindings: serial: renesas: Document RZ/V2N SCIF

Document SCIF bindings for the Renesas RZ/V2N (a.k.a R9A09G056) SoC.
The SCIF interface in Renesas RZ/V2N is identical to the one available
in RZ/V2H(P), so `renesas,scif-r9a09g057` will be used as a fallback,
allowing reuse of the existing driver without modifications.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Acked-by: "Rob Herring (Arm)" <robh@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20250716202923.163950-1-prabhakar.mahadev-lad.rj@bp.renesas.com


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