irqchip/loongson-liointc: Save/restore int_edge/int_pol registers during S3/S4

If int_edge/int_pol registers are configured to not be the default values, we
should save/restore them during S3/S4.

Signed-off-by: Yingkun Meng <mengyingkun@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221207140643.1600743-1-chenhuacai@loongson.cn