dt-bindings: serial: renesas,rsci: Document RZ/N2H support

dt-bindings: serial: renesas,rsci: Document RZ/N2H support

Add documentation for the serial communication interface (RSCI) found on
the Renesas RZ/N2H (R9A09G087) SoC. The RSCI IP on this SoC is identical
to that on the RZ/T2H (R9A09G077) SoC. Therefore, "renesas,r9a09g077-rsci"
is used as a fallback compatible string for RZ/N2H.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20250609192344.293317-1-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>