staging: greybus: gpio: Use irqchip template

staging: greybus: gpio: Use irqchip template

This makes the driver use the irqchip template to assign
properties to the gpio_irq_chip instead of using the
explicit calls to gpiochip_irqchip_add(). The irqchip is
instead added while adding the gpiochip.

Cc: Nishad Kamdar <nishadkamdar@gmail.com>
Cc: Johan Hovold <johan@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20200722074414.48457-1-linus.walleij@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>