memtest86+: Fix DRAM clock calculation for AMD fam 15h

Memory clock frequency is independent from FSB. On AMD Family 15h the
DRAM clock rate only depends on the value of MemClkFreq.

Tested on a custom Bettong board.

Reference:

On Family 15h Models 0-F (page 310):
http://support.amd.com/TechDocs/42301_15h_Mod_00h-0Fh_BKDG.pdf
On Family 15h Models 10-1F (page 345):
http://support.amd.com/TechDocs/42300_15h_Mod_10h-1Fh_BKDG.pdf
On Family 15h Models 30-3F (page 369):
https://support.amd.com/TechDocs/49125_15h_Models_30h-3Fh_BKDG.pdf
On Family 15h Models 60-6F (page 402):
http://support.amd.com/TechDocs/50742_15h_Models_60h-6Fh_BKDG.pdf

Change-Id: I411cb33e50a20b5bf48b43e2accb3378893bd0c3
Credit-to: Alexandre Desnoyers <alex@qtec.com>
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Reviewed-on: https://review.coreboot.org/18090
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Timothy Pearson <tpearson@raptorengineering.com>
1 file changed