gpio: Add helpers to ease the transition towards immutable irq_chip

Add a couple of new helpers to make it slightly simpler to convert
drivers to immutable irq_chip structures:

- GPIOCHIP_IRQ_RESOURCE_HELPERS populates the irq_chip structure
  with the resource management callbacks

- gpio_irq_chip_set_chip() populates the gpio_irq_chip.chip
  structure, avoiding the proliferation of ugly casts

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Bartosz Golaszewski <brgl@bgdev.pl>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220419141846.598305-4-maz@kernel.org