dt-bindings: interrupt-controller: Add Loongson EIOINTC

Add Loongson Extended I/O Interrupt controller binding with DT schema
format using json-schema.

Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/4369959615eda101e612c450b8974d76ce7e8821.1683279769.git.zhoubinbin@loongson.cn