irqchip/loongson-pch-pic: Add suspend/resume support

LoongArch inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5OHOB



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Add suspend/resume support for PCH-PIC irqchip, which is needed for
suspend/hibernation.

Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>