cpu/amd: Fix AMD Family 15h ECC initialization reliability issues

There were numerous issues surrounding AMD ECC initialization on
Family 15h processors due to the incomplete derivation from Family
10h MCT code.  Bring the Family 15h ECC initialization and supporting
setup code in line with the BKDG recommendations.

Change-Id: I7f009b655f8500aeb22981f7020f1db74cdd6925
Signed-off-by: Timothy Pearson <tpearson@raptorengineeringinc.com>
Reviewed-on: http://review.coreboot.org/12003
Tested-by: build bot (Jenkins)
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
8 files changed