Revamp cbmem.py to use the coreboot tables.

Revamp cbmem.py to use the coreboot tables.

This change makes significant changes to cbmem.py to make it use the
coreboot tables to find the memory console and timestamp areas instead
of looking for the in memory table TOC structure. That appears to be
more robust and gets cbmem.py working again after some unrelated
changes that affected memory layout.

It also introduces some small infrastructure to make accessing C style
structures in physical memory easier and more transparent.

Change-Id: I51833055a50c2d76423520ba6e059bf8fc50adea
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: http://review.coreboot.org/762
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>