new_variant: update for volteer fitimage changes

- Add new variables to allow the fitimage binary and versions files
to be in different directories, but the default is that they're in
the same directory.
- Add new files that volteer's commit_fitimage.sh expects to find

BUG=b:179939074
TEST=run new_variant_fulltest.sh for each supported reference board.
Pay special attention to volteer and volteer2.

Change-Id: I0999871b97cccac8cd7506aa1dfe3852ba86cbc3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2806830
Tested-by: Paul Fagerburg <pfagerburg@chromium.org>
Reviewed-by: Nick Vaccaro <nvaccaro@google.com>
Commit-Queue: Paul Fagerburg <pfagerburg@chromium.org>
9 files changed