Documentation: acpi: Add an example for PRP0001

Add an example for the magic PRP0001 device ID which allows matching
ACPI devices against drivers using OF Device Tree compatible property.

Signed-off-by: Thomas Preston <thomas.preston@codethink.co.uk>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>