dt-bindings: interrupt-controller: Add Loongson-2K1000 LIOINTC

Add liointc-2.0 properties support, so update the maxItems and
condition description.

Signed-off-by: Qing Zhang <zhangqing@loongson.cn>
Tested-by: Ming Wang <wangming01@loongson.cn>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>