Define RAMTOP for x86 only

This Kconfig is deprecated, new platforms need to locate
ramstage stack in CBMEM instead.

Change-Id: I20ece297302321337cc2ce17fdef0c55242a4fc3
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/15189
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
5 files changed