fwlib: fix errors with -Wmissing-prototypes

When the fwlib is built with -Wmissing-prototypes and -Werror
there build breakages that occur. Fix these errors by either
including the header file with the correct declaration or provide
the declaration at the top of the c files for global symbols that
are used by tests.

BUG=chrome-os-partner:17695
BRANCH=None
TEST=built fwlib library with -Wmissing-prototypes and -Werror. Also
     'make runtests' still passes.

Change-Id: I992516ee2545509054887173bc65234905381e06
Signed-off-by: Aaron Durbin
Reviewed-on: https://gerrit.chromium.org/gerrit/44042
Reviewed-by: Bill Richardson <wfrichar@chromium.org>
Commit-Queue: Aaron Durbin <adurbin@chromium.org>
Tested-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>
4 files changed