irqchip/dw-apb-ictl: Add primary interrupt controller support

Add support to use dw-apb-ictl as primary interrupt controller.

Suggested-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
[maz: minor fixups]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Tested-by: Haoyu Lv <lvhaoyu@huawei.com>
Link: https://lore.kernel.org/r/20200924071754.4509-4-thunder.leizhen@huawei.com