gpio: sta2x11: use resource management for irqs

Use device resource managed variants of irq_alloc_descs() and
request_irq() and remove the code manually freeing irq resources.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>