Add a variable for allowing alternative firmware

At present the condition for this is checked in one place in
boot_legacy_action(). We need to be able to check it in more than one
place, so put it in a variable when entering developer mode. This matches
how the keyboard UI works.

BUG=chromium:837018
BRANCH=none
TEST=FEATURES=test emerge-grunt --nodeps vboot_reference

Change-Id: Iaf01b827095b0a1139a36af6834eba4dbf7fb150
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1286218
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Reviewed-by: Randall Spangler <rspangler@chromium.org>
1 file changed