detachables: Define VbExDisplayMenu()

Create new callback for drawing detachable firmware menus

BUG=b:35585623
BRANCH=None
TEST=None

Change-Id: Ief207f6119f00151e2d480549aaac3a8755cb1b4
Signed-off-by: Shelley Chen <shchen@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/457838
Reviewed-by: Stefan Reinauer <reinauer@chromium.org>
2 files changed