Use self-locking for mAvailableFeatures

mAvailableFeatures is read-only and set in the constructor. Calls to
hasSystemFeature are often blocked if PM is busy with other operations.

Test: manual - device boots without errors
Bug: 33199244
Change-Id: I5ce0fa7af37e95ac64afb11a1022a27e37c67703
1 file changed