refactor AudioTrack and AudioFlinger createTrack()

Refactor the mechanism used by audio tracks to query and attach
to an output mixer/stream in audio flinger. This will:
- reduce the number of binder transactions needed to create a track
- move sample rate, framecount and flags validations to audio server
side
- move audio session allocation to audio server side
- prepare restriction of certain binder transactions to audioserver only

Test: CTS tests for AudioTrack

Change-Id: If4369aad6c080a56c0b42fbfcc97c8ade17a7439