gpio: mvebu: fix irq domain leak

Uwe Kleine-König pointed out we still have one resource leak in the mvebu
driver triggered on driver detach. Let's address it with a custom devm
action.

Fixes: 812d4788 ("gpio/mvebu: Use irq_domain_add_linear")
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>