test: pid: zone

Add unit-tests for the PID zone module.
Add zone_mock.

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

Change-Id: I51185b2d2daacea6ffb687e8f38c4fe2b2a1bed3
Signed-off-by: Patrick Venture <venture@google.com>
13 files changed