gpiolib: Introduce gpiochip_node_count() helper

The gpiochip_node_count() helper iterates over the device child nodes that
have the "gpio-controller" property set. It returns the number of such nodes
under a given device.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Bartosz Golaszewski <brgl@bgdev.pl>

include/linux/gpio/driver.h

@@ -755,4 +755,15 @@ static inline void gpiochip_unlock_as_irq(struct gpio_chip *gc,
 	device_for_each_child_node(dev, child)					\
 		if (!fwnode_property_present(child, "gpio-controller")) {} else
 
+static inline unsigned int gpiochip_node_count(struct device *dev)
+{
+	struct fwnode_handle *child;
+	unsigned int count = 0;
+
+	for_each_gpiochip_node(dev, child)
+		count++;
+
+	return count;
+}
+
 #endif /* __LINUX_GPIO_DRIVER_H */