irqchip: Add Loongson PCH LPC controller support

mainline inclusion
from mainline-v6.0-rc1
commit ee73f14e
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5OHOB


CVE: NA

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PCH-LPC stands for "LPC Interrupts" that described in Section 24.3 of
"Loongson 7A1000 Bridge User Manual". For more information please refer
Documentation/loongarch/irq-chip-model.rst.

Co-developed-by: Jianmin Lv <lvjianmin@loongson.cn>
Signed-off-by: Jianmin Lv <lvjianmin@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/1658314292-35346-8-git-send-email-lvjianmin@loongson.cn