gpio: dwapb: use a second irq chip

Right new have one irq chip running always in level mode. It would nicer
to have two irq chips where one is handling level type interrupts and
the other one is doing edge interrupts. So we can have at runtime two users
where one is using edge and the other level.

Acked-by: Alan Tull <delicious.quinoa@gmail.com>
Acked-by: Jamie Iles <jamie@jamieiles.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>