gpio: xgene-sb: select IRQ_DOMAIN_HIERARCHY

This driver calls irq_domain_hierarchy() and irq_chip_*_parent().
They are available only when CONFIG_IRQ_DOMAIN_HIERARCHY is enabled.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>