vboot_reference: Add support for 2048-bit exponent 3 keys

This also adds the required tests (keys, testcases).

BRANCH=none
BUG=chromium:684354
TEST=make runtests

Change-Id: I5e148f8792ea325f813d76089271f3c4bcc2935d
Reviewed-on: https://chromium-review.googlesource.com/438951
Commit-Ready: Nicolas Boichat <drinkcat@chromium.org>
Tested-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>
21 files changed