HintManagerService: only check isolated process for app uid

system_server can initiate ADPF session, which may cause deadlock on
chain AMS -> WMS -> graphics -> HintManagerService -> AMS.
This CL is to skip the AMS call when calling from system.

Test: Boot
Bug: 195257481
Signed-off-by: Wei Wang <wvw@google.com>
Change-Id: I6c8f431193b31d7643d3782563b9f6c33fe69da0