factor out common config for k8x8xx's dram_enable() and vt8237r_cfg()

factor out common config for k8x8xx's dram_enable() and vt8237r_cfg()

Instead of writing to config registers in k8x8xx's dram_enable()
and reading those back in vt8237r_cfg(), factor out generation of
the values and reuse that in both places.

Change-Id: I87a37398efe84b33e6678df74cd40b5abfe4f879
Signed-off-by: Florian Zumbiehl <florz@florz.de>
Reviewed-on: http://review.coreboot.org/378
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>