genirq/generic_chip: Export irq_unmap_generic_chip

mainline inclusion
from mainline-v6.0-rc1
commit d319a299
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5OHOB


CVE: NA

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Some irq controllers have to re-implement a private version for
irq_generic_chip_ops, because they have a different xlate to translate
hwirq. Export irq_unmap_generic_chip to allow reusing in drivers.

Signed-off-by: Jianmin Lv <lvjianmin@loongson.cn>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/1658314292-35346-5-git-send-email-lvjianmin@loongson.cn