irqchip/faraday: Fix the trigger types

The triggers in the driver were right for high level triggered
IRQs but the edge detection on edge triggered IRQs was wrong.
After studying a proper driver from Po-Yu Chuang I now know how
to handle these right, and we can properly implement low level
IRQs as well.

The device trees for the Gemini had polarity switched around
so these have been fixed to conform to the right polarity as
well.

Cc: Greentime Hu <green.hu@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>