common.proto: add prefixed ImageType enums

We should be using namespaced enum names here, this commit adds these
new values as well as two new ACCESSORY types.

BUG=chromium:1122854
TEST=./generate.py

Change-Id: Icc803c996550cd148b59fc1817942ab2f5294d7b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/proto/+/2567387
Commit-Queue: George Engelbrecht <engeg@google.com>
Reviewed-by: Jack Neus <jackneus@google.com>
2 files changed