dt-bindings: interrupt-controller: renesas,rzv2h-icu: Document RZ/V2N SoC

Document the Interrupt Control Unit (ICU) used on the Renesas RZ/V2N SoC.

Although the ICU closely matches the design found on the RZ/V2H(P) family,
it differs in its register layout, particularly in the reduced set of
ECCRAM related registers. These variations require a distinct compatible
string so that software can correctly match and handle the RZ/V2N
implementation.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20251127162447.320971-2-prabhakar.mahadev-lad.rj@bp.renesas.com