ACPI: introduce a function to find the first physical device

Factor out the code that finds the first physical device
of a given ACPI device.  It is used in several places.

Signed-off-by: Aleksey Makarov <aleksey.makarov@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/drivers/acpi/internal.h b/drivers/acpi/internal.h
index 1e6833a..8668891 100644
--- a/drivers/acpi/internal.h
+++ b/drivers/acpi/internal.h
@@ -106,6 +106,7 @@
 bool acpi_device_is_battery(struct acpi_device *adev);
 bool acpi_device_is_first_physical_node(struct acpi_device *adev,
 					const struct device *dev);
+struct device *acpi_get_first_physical_node(struct acpi_device *adev);
 
 /* --------------------------------------------------------------------------
                      Device Matching and Notification