dt-bindings: irq: sun7i-nmi: Document the Allwinner A523 NMI controller

The Allwinner A523 SoC contains an NMI controller very close to the one
used in the recent Allwinner SoCs, but it adds another bit that needs to
be toggled to actually deliver the IRQs. Sigh.

Add the A523 specific name to the list of allowed compatible strings.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/all/20250307005712.16828-6-andre.przywara@arm.com