gpio: thunderx: select IRQ_DOMAIN_HIERARCHY instead of depends on

IRQ_DOMAIN_HIERARCHY is not user-configurable, but supposed to be
selected by drivers that need IRQ domain hierarchy support.

GPIO_THUNDERX is the only user of "depends on IRQ_DOMAIN_HIERARCHY".
This means, we can not enable GPIO_THUNDERX unless other drivers
select IRQ_DOMAIN_HIERARCHY elsewhere.  This is odd.  Flip the logic.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: David Daney <david.daney@cavium.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>