ACPI, APEI, Generic Hardware Error Source memory error support

Generic Hardware Error Source provides a way to report platform
hardware errors (such as that from chipset). It works in so called
"Firmware First" mode, that is, hardware errors are reported to
firmware firstly, then reported to Linux by firmware. This way, some
non-standard hardware error registers or non-standard hardware link
can be checked by firmware to produce more valuable hardware error
information for Linux.

Now, only SCI notification type and memory errors are supported. More
notification type and hardware error type will be added later. These
memory errors are reported to user space through /dev/mcelog via
faking a corrected Machine Check, so that the error memory page can be
offlined by /sbin/mcelog if the error count for one page is beyond the
threshold.

On some machines, Machine Check can not report physical address for
some corrected memory errors, but GHES can do that. So this simplified
GHES is implemented firstly.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>