parisc: Add Page Deallocation Table (PDT) support

The firmare in most parisc machines maintains a Page Deallocation Table (PDT)
which holds a list of physical memory addresses where hardware detected memory
errors (single bit and double bit errors).

This patch adds the missing PDC firmware calls and the logic to read the PDT
from firmware, report all current PDT entries and exclude the reported bad
memory from being used by Linux.

Signed-off-by: Helge Deller <deller@gmx.de>