Make sure that we select VIS in the default assitant

In initial boot, and before assistant role is assigned, we need to make
sure that we select the voice interaction service that belongs to the
default assistant set in the OEM config overlay. Previously, we were
selecting the first available VIS which could lead to granting
unnecessary permissions to VIS that won't be used by the system.

Test: atest CtsVoiceInteractionTestCases
Flag: EXEMPT BUFGFIX
Change-Id: I654917495b7fe4742558972f211be20252a28c49
Bug: 442373648