k8 raminit: fix bug, improve clock selection, add clock limit for sock754

k8 raminit: fix bug, improve clock selection, add clock limit for sock754

in amdk8 raminit:
- fix DDR SPD offset for (CLX - 1) (25 instead of 26)
- improve clock/CL selection algorithm
- implement load-dependent clock limiting for socket 754

Change-Id: I5eb8a3e02eaca18f3bef9a98de22f23b23650762
Signed-off-by: Florian Zumbiehl <florz@florz.de>
Reviewed-on: http://review.coreboot.org/377
Tested-by: build bot (Jenkins)
Reviewed-by: Rudolf Marek <r.marek@assembler.cz>