CameraITS: skip checking events if a sensor does not exist

The ITS test_sensor_events and test_unified_timestamps tests check for
accelerometer, compass and gyro events if camera reports real-time
timestamp support. However, some devices may not have certain sensors.
Skip the checking if the corresponding sensor does not exist.

Test: Run ITS on a board without a compass
Bug: 76122643
Bug: 119296003
Change-Id: I9a689a47c92b65bd986a4d8e0c5e4024c1f63409
Merged-In: I9a689a47c92b65bd986a4d8e0c5e4024c1f63409