irqchip/irq-mst: Support polarity configuration

Support irq polarity configuration and save and restore the config
when system suspend and resume.

Signed-off-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com>
[maz: fixed irq_set_type callback]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210315131848.31840-1-mark-pk.tsai@mediatek.com