Make system server profiling an explicit runtime intent

Pass an explicit flag to the runtime when we need to profile the system
server. This ensures that we only start the ProfileSaver and allocate the
code cache when needed.

Test: manual, on a device with system server profiling enabled
Bug: 74081010
Change-Id: I5647e0bfb47d31c0e39bb3f59650cc956f49c4db