Add @SystemApi annotation to internal permissions. (DO NOT MERGE)

This is a first pass at annotating permissions that should not be
granted or used by to third-party apps but that may be required by
privileged system applications.  For this patch, the annotation was
only added to permissions that have a protection level of at least
system.  Signature-only permissions were left alone since they only
need to be visible to built-in components.

Change-Id: I189472028274c133793ad8e4068585c536dd7f38