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

include/linux/gpio/driver.h

@@ -583,6 +583,18 @@ void gpiochip_enable_irq(struct gpio_chip *gc, unsigned int offset);
 int gpiochip_irq_reqres(struct irq_data *data);
 void gpiochip_irq_relres(struct irq_data *data);
 
+/* Paste this in your irq_chip structure  */
+#define	GPIOCHIP_IRQ_RESOURCE_HELPERS					\
+		.irq_request_resources  = gpiochip_irq_reqres,		\
+		.irq_release_resources  = gpiochip_irq_relres
+
+static inline void gpio_irq_chip_set_chip(struct gpio_irq_chip *girq,
+					  const struct irq_chip *chip)
+{
+	/* Yes, dropping const is ugly, but it isn't like we have a choice */
+	girq->chip = (struct irq_chip *)chip;
+}
+
 /* Line status inquiry for drivers */
 bool gpiochip_line_is_open_drain(struct gpio_chip *gc, unsigned int offset);
 bool gpiochip_line_is_open_source(struct gpio_chip *gc, unsigned int offset);