Add code to handle DRAM ECC errors decoding for Fam16h.

Tested on Fam16h with ECC turned on using the mce_amd_inj facility and
works fine.
Signed-off-by: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@amd.com>
[ Boris: cleanups and clarifications ]
Signed-off-by: Borislav Petkov <bp@suse.de>