ACPI: Use ACPICA native way to decode the PLD buffer

This patch is on top of the ACPICA 20120816 release, which implemented
a native way to decode PLD buffer, so use it instead of leting upper
level users do the decoding.

v2: Modify the check for PLD buffer length to reject buffers whose
length < 16

Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>