dt-bindings: soc: renesas: Document SYS for RZ/V2N SoC

dt-bindings: soc: renesas: Document SYS for RZ/V2N SoC

Add the RZ/V2N (R9A09G056) variant to the existing RZ/V2H(P) System
Controller (SYS) binding, as both IPs are very similar.

However, they have different SoC IDs, and the RZ/V2N does not have
PCIE1 configuration registers, unlike the RZ/V2H(P) SYS IP. To handle
these differences, introduce a new compatible string
`renesas,r9a09g056-sys`.

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/20250407191628.323613-4-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>