Make BT HAL audio threads RT

Bluetooth threads that are used in audio have deadline
requirements for glitchless playback.  Those threads need to be
scheduled as RT tasks to ensure that they can meet the deadline even if
there is high system load.  Use schedulerservice to request RT
scheduling.

Bug 37518404
Test:  play Bluetooth audio, check for RT with systrace
Change-Id: I043a97df3d2801922b54dcbf7c700ae11a48c217