Update NotifEvent

All EventTypes should be unique

Test: manual
  1. adb shell device_config put systemui notification.newpipeline.enabled true
  2. adb shell am restart com.android.systemui
  3. Post group notification (go/notify)
  4. adb shell dumpsys activity service com.android.systemui/.SystemUIService \ dependency DumpController NotifLog
  5. Obseve coalesce log

Change-Id: I22b71aa034a801d730aabda615cbc8d986db38c1