hal_adapter: move arc_camera3.mojom to mojo/ folder

Move mojo-related files into a dedicated folder. This is preparation
work for the upcoming camera metadata mojom files.

BUG=b:36358351
TEST=Run `FEATURES=test emerge-<board> arc-camera3` and verify build
     pass.

Change-Id: I9da1f5556d7702264e7fa029f0076f6172c69941
Reviewed-on: https://chromium-review.googlesource.com/456904
Commit-Ready: Ricky Liang <jcliang@chromium.org>
Tested-by: Ricky Liang <jcliang@chromium.org>
Reviewed-by: Ricky Liang <jcliang@chromium.org>
Reviewed-by: Heng-ruey Hsu <henryhsu@chromium.org>
11 files changed