i7core_edac: Use Device 3 function 2 to report errors with RDIMM's

Nehalem and upper chipsets provide an special device that has corrected memory
error counters detected with registered dimms. This device is only seen if
there are registered memories plugged.

After this patch, on a machine fully equiped with RDIMM's, it will use the
Device 3 function 2 to count corrected errors instead on relying at mcelog.

For unregistered DIMMs, it will keep the old behavior, counting errors
via mcelog.

This patch were developed together with Keith Mannthey <kmannth@us.ibm.com>

Signed-off-by: Keith Mannthey <kmannth@us.ibm.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>