Add infrastructure for global data in the CAR phase of boot

Add infrastructure for global data in the CAR phase of boot

The cbmem console structure and car global data are put in their own section,
with the cbmem console coming after the global data. These areas are linked
to be where CAR is available and at the very bottom of the stack.

There is one shortcoming of this change:
The section created by this change needs to be stripped out by the Makefile
since leaving it in confuses cbfstool when it installs the stage in the image.
I would like to make the tools link those symbols at the right location but
leave allocation of that space out of the ELF.

Change-Id: Iccfb99b128d59c5b7d6164796d21ba46d2a674e0
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: http://review.coreboot.org/727
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>