ACPI / property: Add routine for extraction of _DSD properties

Move the extraction of _DSD properties from acpi_init_properties()
to a separate routine called acpi_extract_properties() to make the
subsequent changes more straightforward.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>