amd64_edac: Do not falsely trigger kerneloops

An unfortunate "WARNING" in the message amd64_edac dumps when the system
doesn't support DRAM ECC or ECC checking is not enabled in the BIOS
used to trigger kerneloops which qualified the message as an OOPS thus
misleading the users. See, e.g.

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/422536
http://bugzilla.kernel.org/show_bug.cgi?id=15238

Downgrade the message level to KERN_NOTICE and fix the formulation.

Cc: stable@kernel.org # .32.x
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
Acked-by: Doug Thompson <dougthompson@xmission.com>