gpio: Implement tighter IRQ chip integration

Currently GPIO drivers are required to add the GPIO chip and its
corresponding IRQ chip separately, which can result in a lot of
boilerplate. Use the newly introduced struct gpio_irq_chip, embedded in
struct gpio_chip, that drivers can fill in if they want the GPIO core
to automatically register the IRQ chip associated with a GPIO chip.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Acked-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

include/linux/gpio/driver.h

@@ -100,6 +100,13 @@ struct gpio_irq_chip {
 	 */
 	unsigned int *parents;
 
+	/**
+	 * @map:
+	 *
+	 * A list of interrupt parents for each line of a GPIO chip.
+	 */
+	unsigned int *map;
+
 	/**
 	 * @nested:
 	 *