By default, only eng builds allow latency-test broadcasts

Otherwise, the latency_tracker must be manually
enabled via a SystemConfig (and the device must
minimally be debuggable).

Test: manual
  adb shell device_config put latency_tracker enabled true
  adb shell am broadcast -a com.android.systemui.latency.ACTION_FINGERPRINT_WAKE
Fixes: 227491682
Change-Id: Ia5a7f2f9eec619c26583bcac6b00b8445abdcbf1