irqchip: mtk-sysirq: Add sysirq interrupt polarity support

Mediatek SoCs have interrupt polarity support in sysirq which
allows to invert polarity for given interrupt. Add this support
using hierarchy irq domain.

Signed-off-by: Yingjoe Chen <yingjoe.chen@mediatek.com>
Link: https://lkml.kernel.org/r/1416902662-19281-3-git-send-email-yingjoe.chen@mediatek.com


Signed-off-by: Jason Cooper <jason@lakedaemon.net>