vboot: Don't hardcode special keyboard values.

BUG=chromium:933391
TEST=make runtests
     Test ctrl+d, ctrl+u, and ctrl+l on device
BRANCH=none

Change-Id: Icf8699e5facac44a074cfd47e796b9957fd6b714
Reviewed-on: https://chromium-review.googlesource.com/1475781
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Mathew King <mathewk@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Mathew King <mathewk@chromium.org>
5 files changed