Consolidate registration of HIDL and AIDL HALs

This CL establishes a single flow of registration for both HIDL and
AIDL HALs. The registration of both is done on a separate thread to
avoid blocking system server. Previously, only AIDL registration was
done on a separate thread.

Bug: 184677066
Test: atest CtsBiometricsTestCases
Test: atest AuthServiceTest
Test: atest Fingerprint21Test
Test: atest Face10Test

Change-Id: I4442db15a7b690bb34c6eb7e8793ab4411cbd6d2