gpio: vf610: handle level IRQ's properly

The GPIO IRQ controller is able to generate level triggered
interrupts, however, these were handled by handle_simple_irq so far
which did not take care of IRQ masking. This lead to "nobody cared
(try booting with the "irqpoll" option)" stack traces.

Use the generic interrupt handlers depending on the IRQ type.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>