ACPI: property: Add reference to UEFI DSD Guide

The UEFI DSD Guide specifies a number of GUIDs supported by the _DSD
parser. Point to the DSD Guide in the documentation.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>