gpio: msc313: Convert to immutable irq_chip

gpio: msc313: Convert to immutable irq_chip

Convert the driver to immutable irq-chip with a bit of
intuition.

This conversion follows the pattern of the gpio-ixp4xx
hierarchical GPIO interrupt driver.

Cc: Marc Zyngier <maz@kernel.org>
Acked-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Romain Perier <romain.perier@gmail.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>