Move service registration code into a System API (1/n)

This is an effort to modularize RollbackManager.

AIDL interfaces (IRollbackManager in this case) can’t be used across
module boundaries. We need to add a wrapper around the service
registraction code to expose to SystemServiceRegistry.

The approach is the same as ag/9746851.

Bug: 150347230
Test: m
Change-Id: I83e1cfedf4b4f6bf796e8a4a0ea81d813390f622