Move SmartStorageMaintIdler execution to a separate thread

Sometimes SmartStorageMaintIdler execution takes too much time
because of some Vold global locks contention,
so moving the execution to a separate thread to prevent any ANR.
Bug: 286902553
Test: presubmit

Change-Id: Ie79cc12ac31da51ff7225f076c582bb039f1f42f
2 files changed