arch/x86,lib: make cbmem console work in postcar stage

arch/x86,lib: make cbmem console work in postcar stage

Implement postcar stage cbmem console support. The postcar stage
is more like ramstage in that RAM is already up. Therefore, in
order to make the cbmem console reinit flow work one needs the cbmem
init hook infrastructure in place and the cbmem recovery called.
This call is added to x86/postcar.c to achieve that. Additionally,
one needs to provide postcar stage cbmem init hook callbacks for
the cbmem console library to use. A few other places need to
become postcar stage aware so that the code paths are taken.
Lastly, since postcar is backed by ram indicate that to the
cbmem backing store.

BUG=chrome-os-partner:57513

Change-Id: I51db65d8502c456b08f291fd1b59f6ea72059dfd
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/16619
Tested-by: build bot (Jenkins)
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>