PCI: mediatek: Implement chained IRQ handling setup

Implement irq_chip based solution for IRQs management in order to
comply with IRQ framework.

Signed-off-by: Honghui Zhang <honghui.zhang@mediatek.com>
[lorenzo.pieralisi@arm.com: updated commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Ryder Lee <ryder.lee@mediatek.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>