CBMEM: Tidy up CAR migration

Move the  CAR migration call to arch -specific part of CBMEM init,
it is truly a x86 specific thing.

Change-Id: I715417e54f197b8745e0670d6b900a5660178141
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/7860
Reviewed-by: Aaron Durbin <adurbin@google.com>
Tested-by: build bot (Jenkins)
9 files changed