ContextHubSystemService: Init of ContextHubSystemService in a parallel thread

Expensive parts of initialization (native Initialization) are now done on a separate
init thread.

The service waits for init to complete in PHASE_SYSTEM_SERVICES_READY before expose service.

Test: rebooted and verified that ContextHubSystemService init is completed
Bug: 62667292
Change-Id: I24d7cc7514fcf234a8f97983a9b170da86b0d8be