dt-bindings: i2c: renesas,riic: Document RZ/V2N (R9A09G056) support

dt-bindings: i2c: renesas,riic: Document RZ/V2N (R9A09G056) support

Document support for the I2C Bus Interface (RIIC) found on the Renesas
RZ/V2N (R9A09G056) SoC. The RIIC IP is identical to that on RZ/V2H(P),
so `renesas,riic-r9a09g057` will be used as a fallback compatible,
enabling reuse of the existing driver without changes.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20250501203310.140137-1-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>