gpiolib: Drop unused domain_ops memeber of GPIO IRQ chip

It seems there is no driver that requires custom IRQ chip
domain options. Drop the member and respective code.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>