ACPI: bus: Add iterator for dependent devices

Add a helper macro to iterate over ACPI devices that are flagged
as consumers of an initial supplier ACPI device.

Reviewed-by: Hans de Goede <[e-mail]>
Signed-off-by: Daniel Scally <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

include/acpi/acpi_bus.h

···
 struct acpi_device *acpi_dev_get_next_consumer_dev(struct acpi_device *supplier,
 						   struct acpi_device *start);
 
+/**
+ * for_each_acpi_consumer_dev - iterate over the consumer ACPI devices for a
+ *				given supplier
+ * @supplier: Pointer to the supplier's ACPI device
+ * @consumer: Pointer to &struct acpi_device to hold the consumer, initially NULL
+ */
+#define for_each_acpi_consumer_dev(supplier, consumer)			\
+	for (consumer = acpi_dev_get_next_consumer_dev(supplier, NULL);	\
+	     consumer;							\
+	     consumer = acpi_dev_get_next_consumer_dev(supplier, consumer))
+
 struct acpi_device *
 acpi_dev_get_next_match_dev(struct acpi_device *adev, const char *hid, const char *uid, s64 hrv);
 struct acpi_device *