flashrom: Cleanup internal printf() implementation

This partial back ports elements of the upstream
`commit 1878110848f` and `commit 901a3ba023fd` in
preparation for alignment with the upstream
`commit 1878110848f3`.

BUG=chromium:478356
BRANCH=none
TEST=still builds

Change-Id: I715362f8c149425b8969856533f9490cbb376cc0
Signed-off-by: Edward O'Callaghan <quasisec@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1622047
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Patrick Georgi <pgeorgi@chromium.org>
2 files changed