ACPI / property: Hierarchical properties support update

The definition document of the Hierarchical Properties Extension UUID
for _DSD has been changed recently to allow local references to be
used as sub-node link targets (previously, it only allowed strings to
be used for that purpose).

Update the code in drivers/acpi/property.c to reflect that change.

Link: http://www.uefi.org/sites/default/files/resources/_DSD-hierarchical-data-extension-UUID-v1.1.pdf
Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>