dt-bindings: timer: renesas,ostm: Document RZ/V2N (R9A09G056) support

dt-bindings: timer: renesas,ostm: Document RZ/V2N (R9A09G056) support

Document support for the Renesas OS Timer (OSTM) found on the Renesas
RZ/V2N (R9A09G056) SoC. The OSTM IP on RZ/V2N is identical to that on
other RZ families, so no driver changes are required as `renesas,ostm`
will be used as fallback compatible.

Also update the bindings to require the "resets" property for RZ/V2N
by inverting the logic: all SoCs except RZ/A1 and RZ/A2 now require
the "resets" property.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20250515182207.329176-2-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>