dt-bindings: clock: renesas: Document RZ/V2N SoC CPG

dt-bindings: clock: renesas: Document RZ/V2N SoC CPG

Document the device tree bindings for the Renesas RZ/V2N (R9A09G056)
SoC Clock Pulse Generator (CPG).

Update `renesas,rzv2h-cpg.yaml` to include the compatible string for
RZ/V2N SoC and adjust the title and description accordingly.

Additionally, introduce `renesas,r9a09g056-cpg.h` to define core clock
constants for the RZ/V2N SoC. Note the existing RZ/V2H(P) family-specific
clock driver will be reused for this SoC.

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/20250407191628.323613-7-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>