sb_edac: avoid decoding the same error multiple times

Whenever the extended error reporting is active, multiple MCEs will be
generated for the same event, which will lead to multiple repeated
errors to be reported. So check ADDRV and only decode the error if the
MCE address is valid.

Signed-off-by: Aristeu Rozanski <arozansk@redhat.com>
sb_edac: add support for Ivy Bridge

Since Ivy Bridge memory controller is very similar to Sandy Bridge, it's
wiser to modify sb_edac to support both instead of creating another
driver.

Signed-off-by: Aristeu Rozanski <arozansk@redhat.com>