This fixes a case where the RCD would display transport control
for a RemoteControlClient that didn't have audio focus.
This was happening because registering an RCD was directly calling
the updateRemoteControlDisplay method, without first calling
the checkUpdateRemoteControlDisplay method which verifies the
conditions before updating the display. One of those conditions
is that the audio focus stack shouldn't be empty.
To verify this fix, several functions were also rename to clearly
indicate the lock order and verify we properly synchronize on
the right objects. In doing so, a missing synchronization on
audio focus was found.
Change-Id: If1baaac224ea676aeb83ac0aefcc53f87461c32e
b716f0b7b2