Edge-triggered mode and level-triggered mode need different handlers,
and edge-triggered mode need a specific ack operation. So improve it.

Fixes: ef8c01eb ("irqchip: Add Loongson PCH PIC controller")
Signed-off-by: Chen Zhu <zhuchen@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210805132216.3539007-1-chenhuacai@loongson.cn