Create non updatable system server stubs

Separate out stubs from non-updatable part of the system server. The
ultimate goal is to create system server stubs by merging the
non-updatable stubs and the per-module stubs, instead of generating them
from the combined sources.

Bug: 177640454
Test: m checkapi

Change-Id: Iecb9d51472ae238bbeabe65e1cd782b7c8a4ce59