pinctrl: amd: Use irqchip template

This makes the driver use the irqchip template to assign
properties to the gpio_irq_chip instead of using the
explicit call to gpiochip_irqchip_add().

The irqchip is instead added while adding the gpiochip.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Cc: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
Cc: Sandeep Singh <sandeep.singh@amd.com>
Link: https://lore.kernel.org/r/20200722101545.144373-1-linus.walleij@linaro.org