Introduce config option to initialize CBMEM early.

Introduce config option to initialize CBMEM early.

We want to be able to communicate information between rom and ram
stages of coreboot. This configuration option will be used to
compile such ability in.

Change-Id: I6736fdc264ecd0b63369b28462d7bb96e4c2b012
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: http://review.coreboot.org/710
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>