biod: add proto to biod

Move biod constants into a separate folder and add proto for
signal EnrollScanDone.

BUG=chromium:629657
TEST=biod_client_tool & fake_biometric_tool
CQ-DEPEND=CL:487123, CL:483840

Change-Id: Icb82e0965df0108a32fe0d47927c5c32010da394
Reviewed-on: https://chromium-review.googlesource.com/483939
Commit-Ready: Mengqi Guo <mqg@chromium.org>
Tested-by: Mengqi Guo <mqg@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
6 files changed