ACPI: property: Read buffer properties as integers

Instead of adding a new property type, read buffer properties as integers.
Even though the internal representation in ACPI is different, the data
type is the same (byte) than on 8-bit integers.

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