Improve Audio Playback Capture API

The API too closely resembled the underlying system API, in forcing the
client to construct a full AudioAttribute when only the usage was
useful.

Test: atest android.media.cts.AudioPlaybackCaptureTest#testCaptureMediaUsage
Bug: 111453086
Change-Id: Ic3944120ab4d5dc7b85e5baf7718a39a171a4333
Signed-off-by: Kevin Rocard <krocard@google.com>