ACPI, APEI, GHES: Cleanup ghes memory error handling

Cleanup the logic in ghes_handle_memory_failure(). While at it, add
proper PFN validity check for UC error and cleanup the code logic to
make it simpler and cleaner.

Signed-off-by: Chen, Gong <gong.chen@linux.intel.com>
Acked-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/1385363701-12387-2-git-send-email-gong.chen@linux.intel.com


[ Boris: massage commit message. ]
Signed-off-by: Borislav Petkov <bp@suse.de>