bundle_firmware: Use fmap based CBFS access instead of magic offsets

cbfstool copy also doesn't add the master header by itself anymore, so
let's do it ourselves until we're sure that it isn't used anywhere.

BUG=chromium:445938
TEST=chromeos-bootimage on glados with cbfs regions. Booted.
CQ-DEPEND=CL:313781

Change-Id: I6acb8ddae6124678a6fb782aefb6cfd04fc65ffd
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/313771
Reviewed-by: Patrick Georgi <pgeorgi@chromium.org>
1 file changed