gpio: mt7621: Pass irqchip when adding gpiochip

We need to convert all old gpio irqchips to pass the irqchip
setup along when adding the gpio_chip. For more info see
drivers/gpio/TODO.

For chained irqchips this is a pretty straight-forward
conversion.

This driver requests the IRQ directly in the driver so it
differs a bit from the others.

Cc: Greg Ungerer <gerg@kernel.org>
Cc: Nicholas Mc Guire <hofrat@osadl.org>
Cc: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Cc: Thierry Reding <treding@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: René van Dorst <opensource@vdorst.com>
Link: https://lore.kernel.org/r/20190809141116.16403-1-linus.walleij@linaro.org