ACPI: processor: only evaluate _PDC once per processor

If we evaluate _PDC in the early path, we do not want to evaluate
it again when the processor driver is loaded.

Cc: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>