This patch adds full support to read PDT info on all machine types.  At bootup
the PDT is read and bad memory excluded from usage via memblock_reserve().

Later in the boot process a kernel thread is started (kpdtd) which regularily
checks firmare for new reported bad memory and tries to soft offline pages in
case of correctable errors and to kill processes and exclude such memory in
case of uncorrectable errors via memory_failure().
Signed-off-by: Helge Deller <deller@gmx.de>