ACPI / utils: Add acpi_dev_present()

There's an idiom in use by 7 Linux drivers to detect the presence of a
particular ACPI HID by walking the namespace with acpi_get_devices().
The callback passed to acpi_get_devices() is mostly identical across
the drivers, leading to lots of duplicate code.

Add acpi_dev_present(), the ACPI equivalent to pci_dev_present(),
allowing us to deduplicate all that boilerplate in the drivers.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index be1fc12..407a376 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -39,7 +39,7 @@
 
 static LIST_HEAD(acpi_dep_list);
 static DEFINE_MUTEX(acpi_dep_list_lock);
-static LIST_HEAD(acpi_bus_id_list);
+LIST_HEAD(acpi_bus_id_list);
 static DEFINE_MUTEX(acpi_scan_lock);
 static LIST_HEAD(acpi_scan_handlers_list);
 DEFINE_MUTEX(acpi_device_lock);
@@ -52,12 +52,6 @@
 	acpi_handle slave;
 };
 
-struct acpi_device_bus_id{
-	char bus_id[15];
-	unsigned int instance_no;
-	struct list_head node;
-};
-
 void acpi_scan_lock_acquire(void)
 {
 	mutex_lock(&acpi_scan_lock);