Driver fails to compile in a minimized kernel's configuration because of
the missing dependency on GPIOLIB_IRQCHIP.

 error: ‘struct gpio_chip’ has no member named ‘irq’
   44 |   virq = irq_find_mapping(gpio->gpio_chip.irq.domain, offset);
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Link: https://lore.kernel.org/r/20200106015154.12040-1-digetx@gmail.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>