Refactor LoadFirmware() and LoadKernel() to return VbError_t

BUG=chromium-os:18161
TEST=make && make runtests

Change-Id: I1f60654fef84e26ee15fa8bdaacdb87fb1ddf69e
Reviewed-on: http://gerrit.chromium.org/gerrit/4676
Reviewed-by: Stefan Reinauer <reinauer@chromium.org>
Tested-by: Randall Spangler <rspangler@chromium.org>
9 files changed