dbus: transition to interface for testing

To make testing easier, the dbus objects now receive a
helper interface to use instead of calling into a helper module.

Tested: Ran on quanta-q71l board and it behaved as expected.

Change-Id: I2521d9c75aec76e92d2e26dc044d01011e44d552
Signed-off-by: Patrick Venture <venture@google.com>
8 files changed