ACPI: Add helper acpi_use_parent_companion

In several drivers devices use the ACPI companion of the parent.
Add a helper for this use case to avoid code duplication.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>