Init HotwordDetectionSrvc identity earlier

Grants mic access to the process as soon as it comes up, instead of
waiting for the initialization status callback.

Bug: 190011174
Test: manual - dsp and non-dsp; restarting while invoking the hotword
Test: atest CtsVoiceInteractionTestCases
Change-Id: I54e0b42868f663ae1c9edd9bcf4aaee2a13b827a