move function from header file to .c file

move function from header file to .c file

http://review.coreboot.org/#change,378 introduced a function in k8x8xx.h
move this function to ctrl.c and add a prototype to the header file instead.

Change-Id: I0919ffb2030c53669b95f58b649d4a160f660923
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/429
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>