CBMEM: Always build for x86 romstage

Always build CBMEM for romstage, even for boards that will not use it.
We further restrict car_migrate_variables() runs to non-ROMCC boards without
BROKEN_CAR_MIGRATE.

This fixes regression of commit 71b21455 that broke CBMEM console support
for boards with a combination of !EARLY_CBMEM_INIT && !HAVE_ACPI_RESUME.

Change-Id: Ife91d7baebdc9bd1e086896400059a165d3aa90f
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/7877
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>