audio policy: added audio HAL version in audio_policy.conf

Each hardware module section in audio_policy.conf indicates
the audio HAL version it implements.

Also added a template audio_policy.conf file with examples
of device and gain descriptors added for audio HAL version3.0.

Bug: 14815883.
Change-Id: Id219d121f81f687363f6c18f2d1684b2448dcdf4